Comprehensive CBSE Question Bank in Science X (Term-II)

CBSE II Question Bank in Science CLASS 10 Features Short Answer Type Questions Long Answer Type Questions Strictly Based on the Latest CBSE Term-wise Syllabus Case Study Based MCQs Chapter Summary Very Short Answer Type Questions



Comprehensive CBSE Question Bank in Science Term–II (For Class X)



Comprehensive CBSE Question Bank in Science Term–II (For Class X) (According to the Latest CBSE Examination Pattern) By Dr. N.K. Sharma Nutan Vidya Mandir Dilshad Garden Delhi   laxmi Publications (P) Ltd (An iso 9001:2015 company) bengaluru • chennai • guwahati • hyderabad • jalandhar Kochi • kolkata • lucknow • mumbai • ranchi new delhi

Comprehensive CBSE Question Bank in Science–X (Term-II) Copyright © by Laxmi Publications Pvt., Ltd. All rights reserved including those of translation into other languages. In accordance with the Copyright (Amendment) Act, 2012, no part of this publication may be reproduced, stored in a retrieval system, translated into any other language or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise. Any such act or scanning, uploading, and or electronic sharing of any part of this book without the permission of the publisher constitutes unlawful piracy and theft of the copyright holder’s intellectual property. If you would like to use material from the book (other than for review purposes), prior written permission must be obtained from the publishers. Printed and bound in India Typeset at : Excellent Graphics, Delhi. New Edition ISBN : 978-93-93268-96-9 Limits of Liability/Disclaimer of Warranty: The publisher and the author make no representation or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties. The advice, strategies, and activities contained herein may not be suitable for every situation. In performing activities adult supervision must be sought. Likewise, common sense and care are essential to the conduct of any and all activities, whether described in this book or otherwise. Neither the publisher nor the author shall be liable or assumes any responsibility for any injuries or damages arising here from. The fact that an organization or Website if referred to in this work as a citation and/or a potential source of further information does not mean that the author or the publisher endorses the information the organization or Website may provide or recommendations it may make. Further, readers must be aware that the Internet Websites listed in this work may have changed or disappeared between when this work was written and when it is read. All trademarks, logos or any other mark such as Vibgyor, USP, Amanda, Golden Bells, Firewall Media, Mercury, Trinity, Laxmi appearing in this work are trademarks and intellectual property owned by or licensed to Laxmi Publications, its subsidiaries or affiliates. Notwithstanding this disclaimer, all other names and marks mentioned in this work are the trade names, trademarks or service marks of their respective owners. & Bengaluru 080-26 75 69 30 & Chennai 044-24 34 47 26 Branches & Guwahati 0361-254 36 69 & Hyderabad 040-27 55 53 83 & Jalandhar 0181-222 12 72 & Kochi 0484-405 13 03 & Kolkata 033-40 04 77 79 & Lucknow 0522-430 36 13 Published in India by & Ranchi 0651-224 24 64 Laxmi Publications (P) Ltd. C—00000/021/12 Printed at : Ajit Printing Press, Delhi. (An ISO 9001:2015 Company) 113, GOLDEN HOUSE, GURUDWARA ROAD, DARYAGANJ, NEW DELHI - 110002, INDIA Telephone : 91-11-4353 2500, 4353 2501 www.laxmipublications.com [email protected]

Contents Pages Theme: Materials Unit I: Chemical Substances–Nature and Behaviour 1–40 1. Carbon and its Compounds (NCERT Textbook Chapter-4) 1 2. Periodic Classification of Elements (NCERT Textbook Chapter-5) 13 Theme: The World of Living Unit II: World of Living 41–81 3. How do Organisms Reproduce? (NCERT Textbook Chapter-8) 41 4. Heredity and Evolution (NCERT Textbook Chapter-9) 69 Theme: Natural Phenomena Unit IV: Effects of Current 82–151 5. Electricity (NCERT Textbook Chapter-12) 82 6. Magnetic Effects of Current (NCERT Textbook Chapter-13) 123 Theme: Natural Resources Unit V: Natural Resources 152–168 7. Our Environment (NCERT Textbook Chapter-15) 152



Syllabus Class X Units Evaluation Scheme Marks I Theory 10 II 13 IV Term-II 12 V Chemical Substances-Nature and Behaviour: Chapter 4 and 5 05 World of Living: Chapter 8 and 9 40 Effect of Current: Chapter 12 and 13 Natural Recources: Chapter 15 Total TERM-II Theme: Materials Unit I: Chemical Substances–Nature and Behaviour Chapter–4 Carbon and its Compounds Carbon compounds: Covalent bonding in carbon compounds. Versatile nature of carbon. Homologous series. Chapter–5 Periodic Classification of Elements Periodic classification of elements: Need for classification, early attempts at classification of elements (Dobereiner’s Triads, Newland’s Law of Octaves, Mendeleev’s Periodic Table), Modern periodic table, gradation in properties, valency, atomic number, metallic and non- metallic properties. Theme: The World of the Living Unit II: World of Living Chapter–8 How do organisms reproduce? Reproduction: Reproduction in animals and plants (asexual and sexual) reproductive health-need and methods of family planning. Safe sex vs HIV/AIDS.Child bearing and women’s health. Chapter–9 Heredity and Evolution Heredity: Heredity; Mendel’s contribution- Laws for inheritance of traits: Sex determination: brief introduction.

Theme: Natural Phenomena Unit IV: Effects of Current Chapter–12 Electricity Ohm’s law; Resistance, Resistivity, Factors on which the resistance of a conductor depends. Series combination of resistors, parallel combination of resistors and its applications in daily life. Heating effect of electric current and its applications in daily life. Electric power, Interrelation between P, V, I and R. Chapter–13 Magnetic Effects of Current Magnetic Effects of Current: Magnetic field, field lines, field due to a current carrying conductor, field due to current carrying coil or solenoid; Force on current carrying conductor, Fleming’s Left Hand Rule, Electric Motor, Electromagnetic induction. Induced potential difference, Induced current. Fleming’s Right Hand Rule. Theme: Natural Resources Unit V: Natural Resources Chapter–15 Our Environment Our environment: Eco-system, Environmental problems, Ozone depletion, waste production and their solutions. Biodegradable and non-biodegradable substances.

THEME: MATERIALS UNIT I: CHEMICAL SUBSTANCES—NATURE AND BEHAVIOUR CHAPTER 1: Carbon and its Compounds (NCERT Textbook Chapter-4) SUMMARY OF THE CHAPTER 1. Carbon is tetravalent and easily forms a large variety of compounds on combination with carbon and other atoms by sharing of electrons. It exhibits phenomenon of allotropy, i.e., exists in two or more forms in the same state. For example, graphite and diamond. 2. Covalent bond: When two atoms achieve stability by sharing of an electron pair, each contributes one electron to the electron pair. In this way, the atoms can be regarded as having acquired a noble gas configuration. 3. Covalent compounds: Some atoms share electrons among themselves or with other atoms to attain stable octet configuration. Bonds formed are covalent bonds and the compounds so formed are covalent compounds. Depending on the number of shared pair of electrons, there is single covalent bond, double covalent bond or triple covalent bond. × ×××O× ×× ×O××× × N ×× N × H×H ×× × ×× × ×× H—H OO NN Single covalent Double covalent Triple covalent bond bond bond These compounds have low melting points and boiling points. They do not dissolve in water, do not conduct electricity and are directional in nature. 4. Catenation is the property of carbon to get attached to other carbon atoms. Up to 60 carbon atoms are found to get attached in the shape of a ball (Fullerenes). 5. Allotropy: When an element possesses two or more different forms in the same state, they are called allotropes and the phenomenon is known as allotropy. For example, diamond and graphite are the two allotropes of carbon. 6. Fullerenes: Fullerenes are allotropes of carbon. For example, Buckminsterfullerene is an allotrope of carbon with 60 carbon atoms arranged in the shape of a football. 7. Hydrocarbons: Compounds containing only carbon and hydrogen are called hydrocarbons. 1

2 Science–X 8. Saturated hydrocarbons: Compounds of carbon and hydrogen attached in chains, branches or rings, by single covalent bonds, for example, Alkanes (CnH2n 2): methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10). + 9. Unsaturated hydrocarbons are compounds of carbon and hydrogen with either carbon-carbon double bond (C == C) or carbon-carbon triple bond (C ≡≡ C) in their molecules. For example, 2A):lektehnyens e(C(CnH2H2n2)):, perthopeynnee(C(C2H3H4)4,) panrodpbeuntey(nCe3(HC64)H, b6)u. tene (C4H8). Alkynes (CnH2n _ 10. Functional groups: Groups which determine the chemical nature of an organic compound. In a hydrocarbon, one or more hydrogen atoms are replaced by another element or group. These confer specific properties to the compound regardless of the length and nature of chain and hence are called functional groups. Name of Functional Group Formula of Functional Group Halo —Cl, —Br, —I Alcohol —OH Aldehyde Ketone Carboxylic acid 11. Alkyl radical: The group formed by removal of the hydrogen atom from an alkane molecule is called an alkyl radical or group. 12. Functional group: A group which determines the chemical nature of an organic compound is called a functional group. 13. Homologous series is a group or family of compounds which contain the same functional group but have different chain lengths. Two successive homologues differ by one carbon and two hydrogen atoms in their molecular formulae. 14. Isomerism: In carbon compounds, different compounds are formed with different structures but with the same molecular formula. These compounds are called isomers and the phenomenon is called isomerism. For example, butane (C4H10) can be written as: H3C—CH2—CH2—CH3 (n-butane) and H3C—CH—CH2 (iso-butane) CH3 1. VERY SHORT ANSWER TYPE QUESTIONS [1 Mark] 1. Write the molecular formula of first two members of homologous series having functional group –OH. Ans. CH3OH, C2H5OH

Carbon and its Compounds 3 2. Draw the structural formula of methanoic acid. (CBSE 2016) O Ans. H—C or HCOOH O–H 3. Carbon has four electrons in its valence shell. How does carbon attain stable electronic configuration? (CBSE 2016) Ans. Carbon is tetravalent because it has four valence electrons. In order to achieve noble gas configuration, it shares these electrons with four electrons of other atoms. 4. The formula of citric acid is as follows: COOH CH2 H3C—C—COOH CH2 COOH State the name of –COOH functional group in citric acid. (CBSE 2016) Ans. Carboxylic acid 5. Which of the following belong to the same homologous series? C3H8,C4H8,C4H6,C3H6. (CBSE 2016) Ans. Cfo3rHm6ualnadCCnH4H2n8.belong to the same homologous series which is alkenes with general 6. Which has a triple bond; C2H4, C3H4 and C3H6? (CBSE 2016) Ans. C3H4 has triple bond with the formula CH3C ≡≡ CH. 7. The molecular formula of butane is C4H10. What is the formula of butene? (CBSE 2016) Ans. The formula of butene is C4H8. 8. A compound with molecular formula C3H6O is used as a fuel. Identify the compound. (CBSE 2016) Ans. The compound is ethanol with formula C2H5OH. 9. Write the names of the next homologous of CH3CH2OH and HCOOH. (CBSE 2015) Ans. Propanol and ethanoic acid respectively. 10. Name the second member of alkyne family. Give its structure. (CBSE 2014) Ans. The second member of alkyne family is propyne. Its structural formula is H3C—C≡≡CH. 11. List two characteristic feature of carbon which when put together give rise to a number of carbon compounds. (CBSE 2014) Ans. (i) Catenation (ii) Tetravalency 12. State the valency of each carbon atom in (i) an alkane and (ii) an alkyne. (CBSE 2014) Ans. (i) Valency of carbon atom in an alkane is four. (ii) Valency of carbon atom in an alkyne is four.

4 Science–X 13. Write the molecular formula of benzene and state the number of double bonds in its structure. (CBSE 2014) Ans. (i) The molecular formula of benzene is C6H6. (ii) It contains three double bonds in its structure. 14. The molecular formula of ‘A ’ is C10H18 and ‘B’ is C18H36. Name the homologous series to which they belong? (CBSE 2014) Ans. ‘A’ belongs to alkyne and ‘B’ belongs to alkene. 15. The formula of a hydrocarbon is CnH2n. Name the family to which it belongs and also predict its nature. (CBSE 2013) Ans. The hydrocarbon belongs to alkene family. It is unsaturated in nature. 16. What do we get when ethanoic acid reacts with ethanol in the presence of concentrated sulphuric acid? (CBSE 2013) Ans. Ethyl ethanoate (CH3COOC2H5) is formed by esterification reaction. It has fruity smell. 17. Write the molecular formula of first two members of homologous series having functional group-Cl. (CBSE 2017) Ans. The general formula for the homologous series of functional group –Cl is CnH2n + 1Cl (a) CH3Cl (b) CH3CH2Cl 18. What would be the electron dot structure of carbon dioxide which has the formula CO2? Ans. The electron-dot formula of CO2 is given as: ×× × . C . × ×× O × . . × O ×× ×× 19. What would be the electron dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? Ans. The electron-dot structure of sulphur is made of eight atoms of sulphur in a ring as shown. S SS SS SS S 20. What are the two properties of carbon which lead to the huge number of carbon compounds we see around us? Ans. Two properties of carbon which lead to the huge number of carbon compounds are: (i) Tetravalency (ii) Catenation

Carbon and its Compounds 5 2. SHORT ANSWER TYPE QUESTIONS [2 and 3 Marks] 1. Name the element, other than carbon which exhibits the property of catenation upto seven or eight atoms? Are these compounds stable? (CBSE 2016) Ans. Silicon. No they are very reactive. 2. What is meant by homologous series of carbon compounds? Write the general formula of (i) alkene, and (ii) alkynes. Draw the structures of the first member of each series to show the bonding between the two carbon atoms. (CBSE 2016) Ans. (a) A series of organic compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series. (b) All consecutive members of this series differ by – CH2 unit. (c) Physical properties show gradation but chemical properties are same. (i) CnH2n (ii) CnH2n – 2 HH CC H—C C—H HH 3. The general formula of three compounds A, B, and C is CnH2n. B has highest boiling point and C has lowest boiling point. (i) Mention the type of compounds A, B and C. (ii) Which of these has the minimum number of carbon atoms? (CBSE 2016) Ans. (i) Unsaturated hydrocarbons with double bond. (CBSE 2016) (ii) Compound ‘C’ has minimum number of carbon atoms. 4. List two characteristics of covalent compounds. Ans. (i) Covalent compounds have low melting and boiling points. (ii) Covalent compounds do not conduct electricity. 5. How do diamond and graphite differ in their structures? Is their any effect of structures on the nature of these? (CBSE 2016) Ans. Diamond and graphite are the two crystalline allotropic forms of carbon. But they differ in their structures. In diamond, all the four valence electrons of carbon atom are involved in the covalent bond formation with the electrons of neighbouring carbon atoms. In graphite, only three electrons participate in the bond formation while the fourth electron is free. Diamond without any free electron is a poor conductor of electricity while graphite with free electrons available is a good conductor. 6. Why are alkanes regarded as saturated hydrocarbons while alkenes and alkynes as unsaturated hydrocarbons? (CBSE 2016) Ans. Alkanes contain C—C bonds in the molecules and normal tetrahedral bond angle of 109°28′ is not disturbed. On the other hand, both alkenes and alkynes have a multiple bond (>C = C< or – C ≡ C – bond). The tetrahedral bond angle is no longer present. These are under strain and therefore, unsaturated. 7. List four characteristics of homologous series. (CBSE 2015) Ans. (i) Same functional group. (ii) Similar chemical properties.

6 Science–X (iii) Successive member differ by – CH2 unit/14u./ (iv) Gradation in physical properties. 8. State the meaning of functional group in a carbon compound. Write the functional group present in (i) ethanol and (ii) ethanoic acid and also draw their structures. (CBSE 2015) Ans. An atom or group of atoms which determine the chemical properties of organic compounds are called functional groups. They confer specific properties to the compound, regardless of the length and nature of the carbon chain. S.No. Organic compound Functional group Structure CH3 — CH2 — OH (i) Ethanol Alcohol (—OH) CH3 — COOH (ii) Ethanoic acid Carboxylic acid O —C—OH 9. Give the electron dot structure and structural formula of first member of alkene and alkyne families. (CBSE 2014) HH HH : (ii) H : C :: : C : H or H—C C—H. : Ans. (i) H : C :: C : H or H—C C—H Ethene Ethyne 10. What is homologous series? Which two of the following organic compounds belong to the same homologous series? C2H6, C2H6O, C2H6O2, CH4O (CBSE 2013) Ans. For the definition of homologous series, consult text part. The compounds CH4O and C2H6O belong to the same homologous series known as alkanols. 11. State two characteristic features of carbon which when put together give rise to a large number of carbon compounds. (CBSE 2013) Ans. (i) The size of carbon atom is very small (Atomic radius boads = 77 pm) (ii) The strength of C–C bond is quite high (355 kJ mol–1) Therefore, any number of carbon atoms can be linked by covalent bonds. This self linking property is called catenation. 12. (a) Why are most carbon compounds poor conductors of electricity? (b) Write the name and structure of a saturated compound in which the carbon atoms are arranged in a ring. Give the number of single bonds present in this compound. (CBSE 2018) Ans. (a) In most of carbon compounds, all the electrons take part in the formation of bonds and electrons are not free to move. Therefore, most of carbon compounds are poor conductors of electricity.

Carbon and its Compounds 7 (b) One such saturated compound is cyclobutane and its structure is: It has 12 single covalent bonds. 13. How many structural isomers can you draw for pentane? Ans. Three structural isomers can be drawn for pentane: 14. What will be the formula and electron dot structure of cyclopentane? Ans. The formula of cyclopentane will be aCs5,H10. Its electron-dot structure is written HH HC H CC Or H H HH CC HH 15. What is a homologous series? Explain with an example. Ans. A homologous series is a group of compounds which contain the same functional group but different chain lengths. Thus, these have the same chemical properties but different physical properties. Two adjacent members of a homologous series differ by a CH2 unit. Examples CthHe3tOwHo ,sCam2He5hOoHm,oClo3Hgo7uOsHs,eCri4eHs 9rOesHpeacntidveCl2yH. 4, C3H6, C4H8, C5H10 are members of 16. Draw the electron dot structure of ethyne and also draw its structural formula. Ans. Molecular formula of ethyne is C2H2. Electronic configuration of C = 2, 4 (valence electrons = 4) Electronic configuration of H = 1 (valence electrons = 1)

8 Science–X Electronic dot structure is ×× H ×C ×× C× H ×× Structural formula is H — C ≡≡ C — H Ethyne 17. Identify and name the functional groups present in the following compounds. H HH H HO (a) H—C—C—C—OH (b) H—C—C—C—OH H HH HH HHO HH HHH H (c) H—C—C—C—C—C—H (d) H—C—C—C C—H HH HH HH (b) Carboxylic acid Ans. (a) —OH Hydroxyl Alcohol (c) Ketone (d) —C C— Alkene 18. Carbon, Group (14) element in the Periodic Table, is known to form compounds with many elements. Write an example of a compound formed with (a) chlorine (Group 17 of Periodic Table) (b) oxygen (Group 16 of Periodic Table) Ans. (a) Carbon tetrachloride (CCl4) (b) Carbon dioxide (CO2) 19. In electron dot structure, the valence shell electrons are represented by crosses or dots. (a) The atomic number of chlorine is 17. Write its electronic configuration. (b) Draw the electron dot structure of chlorine molecule. Ans. (a) K L M 287 :: :: (b) :Cl : Cl: 20. Catenation is the ability of an atom to form bonds with other atoms of the same element. It is exhibited by both carbon and silicon. Compare the ability of catenation of the two elements. Give reasons.

Carbon and its Compounds 9 Ans. Carbon exhibits catenation much more than silicon or any other element due to its smaller size which makes the C—C bonds strong while the Si—Si bonds are comparatively weaker due to its large size. 3. LONG ANSWER TYPE QUESTIONS [5 Marks] 1. What are homologous series of compounds? List any two characteristics of homologous series. Ans. Homologous series represents different families of organic compounds into which these are divided. Two characteristics of homologous series are listed. (i) All the members in a particular homologous series of family have the same characteristic functional group. For example, in organic acids, the functional group is carboxyl group (—COOH). (ii) Any two consecutive members in a particular family have the same common dmieffmerbeenrcseofotfhCe Hfa2miinly their molecular formulae. For example, the first three (C3H8). of alkanes are: CH4 (methane), C2H6 (ethane) and propane 2. Explain the nature of the covalent bond using the bond formation in CH3Cl. Ans. Covalent bond is formed by sharing of electrons so that combining atoms complete their outermost shell. In CH3Cl, this happens as: Three hydrogen atoms complete (K = 1 + 1 = 2) their shells by sharing three electrons (one electron each) of carbon atom. Chlorine completes its outer-shell (L = 7 + 1 = 8) by sharing its one out of seven electrons with one electron of carbon atom. Thus, carbon atom shares all its four electrons with three hydrogen atoms and one of chlorine atom and complete its outer shell (L = 4 + 3 + 1 = 8). 3. Draw the electron dot structures for (a) ethanoic acid (b) H2S (c) propanone (d) F2 Ans. (a) Ethanoic acid (b) H2S H ×. .. .× H .S.

10 Science–X (c) Propanone (d) F2 4. (a) What are hydrocarbons? Give examples. (b) Give the structural differences between saturated and unsaturated hydrocarbons with two examples each. (c) What is a functional group? Give examples of four different functional groups. Ans. (a) Compounds of carbon and hydrogen are called hydrocarbons. Example: methane, ethane, etc. (b) Saturated hydrocarbons contain carbon-carbon single bonds. Unsaturated hydrocarbons contain at least one carbon-carbon double or triple bond. H HH HH H—C—H H—C—C—H CC H—C C—H HH H HH Ethyne Ethene Methane Ethane Saturated hydrocarbons Unsaturated hydrocarbons (c) Functional group: An atom or a group of atoms joined in a specific manner which is responsible for the characteristic chemical properties of the organic compounds. Examples are hydroxyl group (—OH), aldehyde group (—CHO), carboxylic group (—COOH), etc. 4. CASE STUDIES Read the passages carefully answer the questions that follow. 1. The element carbon occurs in different forms in nature with widely varying physical properties. Both diamond and graphite are formed by carbon atoms, the difference lies in the manner in which the carbon atoms are bonded to one another. In diamond, each carbon atom is bonded to four other carbon atoms forming a rigid three- dimensional structure. In graphite, each carbon atom is bonded to three other carbon atoms in the same plane giving a hexagonal array. One of these bonds is a double- bond, and thus the valency of carbon is satisfied. Graphite structure is formed by the hexagonal arrays being placed in layers one above the other. Answer the following questions: (i) The electronic configuration of Carbon atom is (a) 2, 6 (b) 2, 8 (c) 2, 4 (d) 2, 3 (ii) Which allotropic form of carbon is good conductor of electricity? (a) Diamond (b) Graphite (c) Buckministerfullerence (d) All of these

Carbon and its Compounds 11 (iii) The property by which a large number of atoms of the same element get linked through covalent bonds forming long chain is called: (a) catenation (b) polymerisation (c) allotropy (d) addition reaction (iv) Which of the following compounds will give a non-luminous flame on burning? (a) Spirit (b) Camphor (c) Naphthalene (d) Benzene 2. Carbon has the unique ability to form bonds with other atoms of carbon, giving rise to large molecules. This property is called catenation. These compounds may have long chains of carbon, branched chain of carbon or even carbon atoms arranged in rings. In addition, carbon atoms may be linked by single, double or triple bonds. Compounds of carbon, which are linked by only single bonds between the carbon atoms are called saturated compounds. Compounds of carbon having double or triple bonds between their carbon atoms are called unsaturated compounds. Answer the following questions: (i) Which other properties of carbon is responsible for its unique nature? (a) Tetravalency (b) Small size of carbon atom (c) both (a) and (b) (d) none of these (ii) Why is carbon tetrachloride not a good conductor of electricity? (a) due to absence of ions (b) being covalent compound (c) comprises of only atoms (d) All of these (iii) Select the saturated hydrocarbons from the following: C2H4, C6H14, C4H10, C3H6 (b) C6H14 and C3H6 (a) C6H14 and C4H10 (c) C6H14 and C4H10 (d) none of these (iv) Select the compounds not having covalent bonds: CaCl2, NH3, CH4, CCl4 (a) NH3 (b) CH4 (c) CCl4 (d) none of these 3. The presence of a functional group decides the properties of the carbon compound, regardless of the length of the carbon chain. The series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series. As the molecular mass increases in any homologous series, a gradation in physical properties is seen. This is because the melting and boiling points increase with increasing molecular mass. Other physical properties such as solubility in a particular solvent also show a similar gradation. But the chemical properties, which are determined solely by the functional group, remain similar in a homologous series. Answer the following questions: (i) Write the next two homologoues of propene. (a) Ethene and Butene (b) Butene and Pentene (c) Pentene and Hexene (d) none of these (ii) How much is the difference in mass between any two consecutive homologues? (a) 10u (b) 12u (c) 14u (d) 16u

12 Science–X (iii) Which of the following is not a pair of the same homologous series? (a) CH3CH2CH2OH, CH3CH2Cl (b) CH3CH2COOH, CH3COOH (c) CH3CH3, CH4 (d) C2H4, C3H6 (iv) The general formula for the homologous of alkynes. (a) CnH2n (b) CnH2n–2 (c) CnH2n+2 (d) none of these 4. Carbon and its compounds are of immense use to mankind. Any compound which on burning gives a black substance is known to be made from carbon. Food, clothes, medicines, books, plastics, and many more things—all contain carbon. Carbon is a very versatile element. A small amount of carbon occurs as free element in the earth’s crust. The earth’s crust has only 0.02% carbon in the form of minerals (like limestone, coal and petroleum) and in the atmosphere as carbon dioxide (0.03%). It is contained in proteins, carbohydrates and other compounds that make up living things. In spite of this small amount of carbon available in the nature, its importance seems to be immense. (i) How many electrons are shared by each atom in the formation of a double bond? (a) Four (b) Five (c) Six (d) Two (ii) The atomic number of carbon is 6. Write its electronic configuration. (a) 1, 2, 3 (b) 2, 2, 2 (c) 2, 4 (d) none of these (iii) Diamond is the hardest substance because each atom is held in place by ...... strong bonds. (a) two (b) three (c) four (d) six (iv) Name the functional group present in the compound HCOOH. (a) Carboxylic acid group (b) Aldehydic group (c) Ketonic group (d) none of these Answers 1. (i) (c) 2, 4 (ii) (b) Graphite (iii) (a) catenation (iv) (a) Spirit 2. (i) (c) both (a) and (b) (ii) (d) All of these (iii) (a) C6H14 and C4H10 (iv) (d) none of these 3. (i) (b) Butene and Pentene (ii) (c) 14u (iii) (a) CH3CH2CH2OH, CH3CH2Cl (iv) (b) CnH2n–2 4. (i) (a) Four (ii) (c) K L 24 (iii) (c) Because each atom is held in place by four strong bonds. (iv) (a) Carboxylic acid group

THEME: THE WORLD OF LIVING UNIT II: WORLD OF LIVING CHAPTER 3: How do Organisms Reproduce? (NCERT Textbook Chapter-8) SUMMARY OF THE CHAPTER 1. Reproduction: This process is very important as it ensures the continuation of similar kinds of individuals, generation after generation. 2. Modes of reproduction: There are two modes of reproduction: (i) Sexual reproduction (ii) Asexual reproduction 3. Sexual reproduction: Reproduction resulting from the fusion of male and female gametes. 4. Asexual reproduction: Reproduction in which only a single parent is involved. 5. DNA found in chromosomes in the nucleus of the cells has the information to create proteins which lead to body design of an organism. 6. Variation: It is useful for the survival of species over time. 7. Types of asexual reproduction: (i) Fission: It is the cell division occurring in unicellular organisms. It involves splitting of the cell into two individual cells. (ii) Fragmentation: This type of reproduction occurs in multicellular organisms with simple body organisation which break into parts and each part grows into new individual. (iii) Regeneration: Multicellular fully differentiated organisms have the capacity to regenerate full body from a part of their body. (iv) Budding: In organisms like hydra, a bud develops as an outgrowth due to repeated cell division at specific site which after developing into tiny individuals detaches from the body of the parent to become a new individual. (v) Vegetative propagation: In plants various parts such as roots, stem and leaves can regenerate full individual plant under suitable conditions. (vi) Spores formation: Many fungi propagate by means of spores. 8. Sexual reproduction in plants: Sexual reproduction in angiosperms is by means of flowers. Flowers are reproductive parts which have sepals, petals, stamens and carpels. 41

42 Science–X 9. The seed contains the future plant or embryo which develops into a seedling under appropriate conditions. This process in known as germination. 10. Unisexual flowers: The flowers which either contain only the pistil or only the stamens. 11. Bisexual flowers: The flowers which contain both stamens and pistil are called bisexual flowers. 12. Reproduction: Male reproductive organs are a pair of testes, sperm ducts and a penis. Female reproductive organs are a pair of ovaries, oviducts and uterus. 13. Contraception: In human beings, contraception to avoid pregnancy can be achieved by the use of condoms, oral pills, copper-T and other methods. 1. VERY SHORT ANSWER TYPE QUESTIONS [1 Mark] 1. How does plasmodium reproduce. In this method sexual or asexual? Ans. Multiple fission; Asexual. 2. Where is DNA found in a cell? (CBSE 2016) Ans. Genes/Chromosomes 3. Why cannot all multicellular organisms divide cell-by-cell like spirogyra? (CBSE 2016) Ans. The higher multicellular organisms have differentiation of structure and function unlike spirogyra in which all the cells are similar and independent units. 4. Name the two plants which are grown using plant tissue culture method. (CBSE 2016) Ans. (i) Orchids (ii) Asparagus 5. Name some plants which are usually propagated by cutting method. (CBSE 2016) Ans. Rose, cactus, sugarcane, pineapple 6. What is the function of pollen grains in flowers? (CBSE 2016) Ans. Pollen grains fertilise the egg cell present in the embryo sac of an ovule. 7. State an advantage of vegetative propagation. (CBSE 2015) Ans. This method can be practised for growing such plants which usually do not produce seeds or produce non-viable seeds. 8. Name the type of cells which undergo regeneration. (CBSE 2015) Ans. Specialised cells called regenerative cells which can proliferate and make large number of cells. 9. Name two organisms having the ability of regeneration. (CBSE 2015) Ans. Hydra and Planaria 10. Name two plants that reproduce through spores. (CBSE 2015) Ans. Mushrooms and ferns 11. State how the copper-T serves as an effective contraceptive device. (CBSE 2015) Ans. Copper-T is placed inside the uterus by a doctor, which prevents implantation in the uterus. 12. How can the chromosomes be identified? (CBSE 2014) Ans. Chromosomes can be seen as thread-like structures when cell divides.

How do Organisms Reproduce? 43 13. List two functions performed by ovaries in a human female. (CBSE 2014) Ans. (i) Production of ovum (gamete). (ii) Secretion of female hormones (estrogen and progesterone). 14. Why is DNA copying an essential part of the process of reproduction? (CBSE 2014) Ans. DNA is an essential part because errors in DNA copying leads to variation which not only gives survival advantage to an organism but also leads to evolution. 15. Why is temperature of scrotal sac 2°C less than the body temperature? (CBSE 2014) Ans. It is less because testes require temperature 2°C less than the body temperature for the production of sperms. 16. Which group of plants shows double fertilisation? (CBSE 2014) Ans. Angiosperms 17. What happens during pollination? (CBSE 2013) Ans. Pollen grains from stamen get transferred to carpels. 18. Mention one physiological advantage of grafting quality roses on wild rose stock. (CBSE 2013) Ans. The rose stock is derived from a plant resistant to diseases and pests and is efficient in absorption of water and minerals. 19. Why is sexual reproduction considered to be superior to asexual reproduction in terms of evolution? (CBSE 2013) Ans. Sexual reproduction is a source of variation which ensures survival of the species. 20. Why is regeneration considered a method of reproduction? (CBSE 2013) Ans. Regeneration is considered a method of reproduction because an entire new organism can be made from its fragmented body. 21. Write one example of a plant showing vegetative propagation by leaves. (CBSE 2013) Ans. Bryophyllum 22. Name the method by which spirogyra reproduces under favourable conditions. Is this method sexual or asexual? (CBSE 2017) Ans. Under favourable conditions, spirogyra reproduces by fragmentation. This is an asexual method of reproduction. 23. What are the changes seen in girls at the time of puberty? Ans. The females show development of breasts, darkening of nipples, menstruation and growth of public hair. 24. In a bisexual flower in spite of the young stamens being removed artificially, the flower produces fruit. Provide a suitable explanation for the above situation. Ans. The pistil is intact. Cross pollination has occurred leading to fertilisation and formation of fruit. 25. Can you consider cell division as a type of reproduction in unicellular organism? Give one reason. Ans. Yes, because it results in the formation of two daughter cells, that is, it results in the production of more individuals of the organism.

44 Science–X 26. Colonies of yeast fail to multiply in water, but multiply in sugar solution. Give one reason for this. Ans. Sugar provides energy for sustaining all life activities in yeasts. In water, it fails to reproduce because of inadequate energy in its cells. 27. Give two reasons for the appearance of variations among the progeny formed by sexual reproduction. Ans. (a) Sexual reproduction involves two parents with different sets of characters. (b) The gene combinations are different in gametes. 28. In tobacco plant, the male gametes have twenty-four chromosomes. What is the number of chromosomes in the female gamete? What is the number of chromosomes in the zygote? Ans. Number of chromosomes in female gamete is 24. Number of chromosomes in zygote is 48. 29. Why cannot fertilisation take place in flowers if pollination does not occur? Ans. In a flower fertilisation requires both male and female gametes. If pollination does not occur, male gamete is not available hence fertilisation cannot take place. 30. Is the chromosome number of zygote, embryonal cells and adult of a particular organism always constant? How is the constancy maintained in these three stages? Ans. Yes, the constancy is maintained because cells in all these three structures undergo only mitotic divisions. 31. Where is the zygote located in the flower after fertilization? Ans. Zygote is located inside the ovule which is present in the ovary. 32. What changes are observed in the uterus if fertilisation does not occur? Ans. The thick and spongy lining of the uterus slowly breaks and comes out through the vagina as blood and mucus. 33. Green and red coloured seeds are recessive and dominant traits respectively. Out of Fhy1barnidd?F2 in which generation will the green seed appear, if both parents are not Ans. F2 generation. 34. What is self sterility mechanism in flowers which allows only cross-pollination? Ans. In self sterility, pollen grains of the same flower are not capable to fertilise that flower, e.g. potato, tea etc. Hence, cross-pollination is the rule applied. 35. Colonies of yeast fail to multiply in water, but multiply in sugar solution. Give one reason for this. Ans. Sugar provides energy for sustaining all life activities in yeast. In water, it fails to reproduce because of inadequate energy in its cells. 36. What is the main cause of variations among organisms during sexual reproduction? Ans. During sexual reproduction, the DNA copying mechanism is not accurate, and the resultant errors are a source of variations in populations of organisms.

How do Organisms Reproduce? 45 2. SHORT ANSWER TYPE QUESTIONS [2 and 3 Marks] 1. What happens when: (a) Accidently, planaria gets cut into many pieces? (b) Bryophyllum leaf falls on the wet soil? (c) On maturation sporangia of Rhizopus bursts? Ans. (a) Each piece regenerates into new Planaria (b) Bud, at its notches develop into new plants. (c) It releases spores which germinate into new mycelium in moist conditions. 2. List any four steps involved in sexual reproduction and write its two advantages. Ans. Steps of Sexual Reproduction: • Formation of male and female gametes • Transfer of male gamete to female gamete • Fusion of gametes resulting in zygote formation • Zygote grows into an embryo forming a new individual Advantages: • Increases genetic variation • Plays an important role in the origin of new species 3. State the changes that take place in the uterus when: (a) Implantation of embryo has occured. (b) Female gemete/egg is not fertilised. Ans. (a) When implantation of embryo has occurred the uterine wall thicknes and is richly supplied with blood to nourish the growing embryo. (b) The thick and spongy lining of the uterus slowly breaks and comes out through the vagina as blood and mucus. 4. List any two modes of asexual reproduction in animals. Under which mode of reproduction is vegetative propagation placed and why? List two advantages of vegetative propagation. (CBSE 2016) Ans. Two asexual modes of reproduction in animals are: Fission/Fragmentation/Budding/Regeneration (Any Two) Vegetative propagation is under asexual mode of reproduction. Reasons: Reproductive part of the plant not involved/Single parent involved. Advantages of vegetative propagation (Any two) (i) Plants raised can bear flowers and fruits earlier than those produced from seeds. (ii) Plants that have lost the capacity to produce seeds can be produced. (iii) All plants produced are genetically similar to the parent plant. 5. State two examples each of the following: (a) Plants having unisexual flowers (b) Agents of pollination (c) Physical changes that are common to both boys and girls. (CBSE 2016) Ans. (a) Papaya, watermelon (b) Wind, water, air, insects (any two)

46 Science–X (c) (i) Increase in height and weight. (Body becomes larger) (ii) Thinner hair appears on legs, arms as well as on the face. (iii) Skin becomes oily and pimples develop. 6. What is placenta? State its function in human female. (CBSE 2016) Ans. Placenta: A special tissue embedded in the uterus wall with the help of which human embryo gets nutrition from mother’s blood. Functions: 1. To provide large surface area for glucose and O2 to pass through mother’s blood to the embryo. 2. To metabolic waste generated by embryo is removed through placenta into mother’s blood. 7. Variations are important for the survival of species over time. Justify this statement with reasons. (CBSE 2016) Ans. Variations help the individuals to survive even after the drastic changes occur in nature. These changes may be in the niche, temperature, salinity or water levels, etc. 8. Mention the changes seen in the girls that depict the aspect of the sexual maturation of the body? (CBSE 2016) Ans. (i) Growth of pubic hair. (armpits and the genital area) (ii) Breast size begins to increase with darkening of the skin of the nipples at the tips of the breast. (iii) The hips widen. (iv) Menstruation starts. 9. Justify the following statements: (a) Variations are beneficial for the species over a period of time. (b) New offspring produced are similar to their parents but not identical. (c) Binary fission is different in Amoeba and Leishmania. (CBSE 2015) Ans. (a) Variations are beneficial for species because they give survival advantage even in the adverse environmental conditions. (b) Similar—Same DNA Not identical—Due to variation during DNA copying (c) Amoeba—Any plane; Leishmania—definite orientation. 10. Name and explain the method by which rhizopus reproduces. (CBSE 2013, 2015) Ans. Rhizopus reproduces by spore formation. Method: Sporangium It is a method of asexual reproduction. Spore formation in Rhizopus Spores are produced in a structure called sporangium. The nucleus divides several times within the sporangium and each nucleus with a bit of cytoplasm, develops into a spore.

How do Organisms Reproduce? 47 11. What is the effect of DNA copying, which is not perfectly accurate, on the reproduction process? How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals? (CBSE 2014, 2015) Ans. (i) DNA copying leads to more variations in the offspring. (ii) Sexually reproducing organisms have special lineage of cells which have only half the amount of DNA/half the number of chromosomes as the parent cell. (iii) When such germ cells fuse, a new individual is formed with the same amount of DNA as that of parent. 12. Explain how organisms create an exact copy of themselves. (CBSE 2015) Ans. To build the copies of DNA or the genetic material, the cells use biochemical reactions. Additional cellular apparatus along with the DNA copies are separated and so a cell divides to give rise to two almost identical cells. 13. State the changes that take place in the uterus subsequent to implantation of young embryo. How does this embryo get nourishment inside the mother’s body? (CBSE 2013, 2015) Ans. (i) The uterine wall thickens, i.e., richly supplied with blood. (ii) A special tissue called placenta develops which connects embryo to the uterine wall that provides nutrients and oxygen to it. (iii) Placenta is a disc which is embedded in the uterine wall. It contains villi on the embryo’s side of the tissue. On the mother’s side are blood spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo. 14. (a) What is the location of the following: (i) DNA in a cell (ii) Gene (b) Expand DNA. (CBSE 2014) Ans. (a) (i) In the nucleus of cell. (ii) Located on the chromosomes. (b) Deoxyribonucleic acid 15. What are chromosomes? Explain how in sexually reproducing organisms, the number of chromosomes in the progeny is maintained? (CBSE 2014) Ans. Chromosomes are thread-like structures made up of DNA found in the nucleus. The original number of chromosomes becomes half during gamete formation. Hence, when the gametes combine, the original number of chromosomes gets restored in the progeny. 16. (a) What are sexually transmitted diseases? Name any one which is caused by bacteria and one caused by viral infection. (b) Mention any two methods to avoid such diseases. (CBSE 2014) Ans. (a) Diseases that spread through the sexual contact are called sexually transmitted diseases. (i) gonorrhoea or syphilis (ii) warts, HIV, AIDS (b) (i) Use of condoms on penis. (ii) Use covering on vagina.

48 Science–X 17. Differentiate between plumule and radicle. (CBSE 2014) Ans. Plumule Radicle (i) The part of growing embryo which (i) The part of growing embryo which later later forms the shoot of young plant. forms the root of young plant. (ii) It is positively phototrophic and (ii) It is positively geotrophic and negatively negatively geotrophic. phototrophic. 18. Explain the process of regeneration in planaria. How is this process different from reproduction? (CBSE 2013, 2014) Ans. Planaria gets cut into many pieces, each piece grows into separate individual, specialized cells proliferate. Mass of cells gets differentiated into various cells and tissues. Regeneration is not the same as reproduction as most of the organisms would not normally depend on being cut up to be able to reproduce. (It is normally for repair of the damaged part.) 19. Distinguish between the functions of ovary and testis. (CBSE 2013, 2014) Ans. Ovary Testis (i) Testis is the primary sex organ in males (i) Ovary is the primary sex organ in females which produces eggs. which produces sperms. (ii) It also secretes hormone testosterone (ii) It also secretes hormone such as estrogen (which imparts female which imparts male secondary sexual secondary sexual characters) and characters. progesterone (which maintains pregnancy). (iii) Testis remains functional even more than 70 years of age. (iii) Ovary remains functional up to 50 years of age. (CBSE 2013, 2014) 20. Differentiate between the following: (a) Placenta and uterus (b) Unisexual and bisexual flowers (c) Fertilization and germination Ans. (a) Placenta Uterus The embryo gets nutrition from After fertilization, embryo gets attached to the the mother’s blood with the help walls of uterus. of a special tissue called placenta. (b) Unisexual flowers Bisexual flowers Flowers which contain either Flowers which contain both stamens and stamens or carpels. carpels. (c) Fertilization The fusion of male gamete with Germination female gamete leading to the The growth of embryo (present in the seed) into formation of zygote is known as seedling under appropriate conditions is known fertilization. as germination.

How do Organisms Reproduce? 59 11. (a) Write the function of following parts in human female reproductive system: (i) Ovary (ii) Oviduct (iii) Uterus (b) Describe in brief the structure and function of placenta. (CBSE 2018) Ans. (a) Functions of Ovary (i) Formation of female gametes called ova. (ii) Release of female sex hormones estrogen and progesterone. Functions of Oviduct (i) To receive matured ovum from ovary. (ii) Fertilisation occurs in oviduct. Functions of Uterus (i) Embryonic development occurs till birth. (ii) Implantation of embryo occurs. (b) Placenta is a disc like special tissue develops between the uterine wall and the embryo. It links the embryo to the mother through umbilical cord. Functions of Placenta (i) It supplies nutrients from mother’s blood to the developing foetus. (ii) Exchange of O2 and CO2 takes place through placenta. (iii) Excretion from embryo takes place through placenta. (iv) It stores nutrients like fat, glycogen for embryo before formation of lives. 12. (a) Name the organ that produces sperms as well as secretes a hormone in human males. Name the hormone it secretes and write its functions. (b) Name the parts of the human female reproductive system where fertilisation occurs. (c) Explain how the developing embryo gets nourishment inside the mother’s body. (CBSE 2017) Ans. (a) The organ that produces sperms as well as secreted male hormones is testis. The hormone secreted by it is testosterone. Its important functions are as follows: (i) It stimulates sperm production. (ii) It stimulates the development of secondary sexual characters in males like growth of facial hairs, low pitch voice, etc. (iii) It involves the development, maturation and functioning of male accessory sex organs like vas deferens and seminal vesicles. (b) In human females reproductive system, the process of fertilisation takes place in one of the fallopian tubes. (c) The embryo gets nutrition from the mother’s blood with the help of a special tissue called placenta. Placenta is a vascular membranous organ that connects the developing foetus to the uterine wall of the mother. It contains villi on the embryo’s side of the tissue. This provides a large surface area for glucose and oxygen to pass from mother to the embryo. The placenta draws nourishment and oxygen, which it supplies to the foetus, from the maternal circulation. In turn, the placenta receives carbon dioxide and wastes of fetal metabolism and discharges them into the maternal circulation for disposal. 13. (a) Define vegetative propagation. List its two methods. (b) Why is this mode practised for growing some types of plants?

60 Science–X (c) Explain the process of budding in Hydra with the help of labelled diagrams. (CBSE 2019) Ans. (a) Reproduction through vegetative parts of a plant like roots/stem/leaves/Artificial/ Layering/Grafting (any two) (b) (i) In some plants which produce non-viable seeds. (ii) It consumes less time/fast method. (c) Budding in hydra: 14. What is the importance of DNA copying in reproduction? Ans. Reproducing organisms create new individuals that look very much like themselves. The daughter organisms and their parents look similar because their body design is similar. Reproduction at its most basic level involves making copies or the blueprint of the body design. The chromosomes in the nucleus of a cell contain information for inheritance of features from parents to the next generation in the form of DNA (Deoxyribonucleic Acid, molecules). So, reproducing cells prepare copies of DNA molecule to keep one DNA copy with the parent cell and other copy/copies to pass on the next generation/daughter cells. 15. Why is variation beneficial to the species but not necessary for the individual? Ans. A variation may not be beneficial for an individual that is not suitable to the niche. In this case an individual or a few variants may not survive. This does not affect existence of a species. Variations are useful for the survival of species in changed environmental situations. For example, if a population of reproducing organisms were suited to a particular niche (well defined place of abode) and if the niche is drastically changed, the population could be wiped out. However, if some variations were to be present in a few individuals in these populations, there would be some chance for them to survive. 16. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration? Ans. In highly developed multicellular organisms, different cell types perform different specialised functions. Reproduction in such organisms is also the function of a specific cell type. If the organism itself consists of many cell types, reproduction by regeneration or fragmentation cannot be achieved.

How do Organisms Reproduce? 61 In multicellular organisms like Hydra and Planaria regeneration is carried out by specialised cells. These cells proliferate and make large numbers of cells. From this mass of cells, different cells undergo changes to become various cell types and tissues. Such specialised cells which can regenerate or develop a new individual from their body part do not exist in complex organisms. 17. Why is DNA copying an essential part of the process of reproduction? Ans. Reproducing organisms create new individuals that look very much like themselves. They look similar because their body designs are similar. The DNA present in chromosomes located in the nucleus of a cell, contains information for inheritance of features from parents to next generation. So, reproducing cell creates two copies of the DNA. One copy of DNA remains in the reproducing original cell. The other copy of DNA is passed to daughter cell formed by parent having additional cellular apparatus. 18. What are the advantages of sexual reproduction over asexual reproduction? Ans. Sexual reproduction incorporates the process of combining DNA from two different individuals during reproduction. Sexual reproduction promotes variation among the offspring of the same parents and provides opportunities for new combination of characters, thus playing an important role in the origin of new species. Asexual reproduction does not require combination of DNA from two different individuals. So, it does not create variations and does not help in creating new species and evolution. 19. What are the different methods of contraception? Ans. The methods used for regulation of child birth are: (i) Barrier method: In this method physical devices like condom, cervical caps and diaphragm are used to prevent sperms to reach upto the ovum. (ii) Chemical method: In this method specific drugs are used by females. These drugs may be (a) oral pills or (b) vaginal pills. Oral pills mainly contain hormones and are called oral contraceptives. (iii) Intrauterine contraceptive devices (IUCDs): IUCD like Copper-T is placed safely in the uterus by a skilled doctor. IUCDs prevent implantation of the fertilized ovum inside the uterus. (iv) Surgical method: This method is applicable to both male and female. In males, a small portion of vas deferens and in females the fallopian tube is surgically removed or ligated (tied). It is known as vasectomy in males which prevents release of sperms from the testis. In females, it is called tubectomy. 20. How are the modes for reproduction different in unicellular and multicellular organisms? Ans. The modes of reproduction in unicellular organisms are: (i) Binary fission is found in unicellular animals like Amoeba, Paramecium, Euglena, etc. After attaining an optimum size the adult individual undergoes a simple division into two daughters of equal size. It consists of division of the nucleus followed by cleavage of cytoplasm into equal parts, each having a daughter nucleus. Binary fission can occur in any place in Amoeba. (ii) Multiple fission is also a mode of asexual reproduction found in unicellular animals or protozoans, e.g., Plasmodium, Monocystis. The nucleus of the parent cell undergoes repeated divisions to produce a number of daughter nuclei. The

62 Science–X cytoplasm cleaves around each nucleus to form many daughter cells. Ultimately under favourable conditions, parent cell membrane ruptures and daughter individuals are released. Sometimes, the daughter cells derived from a multiple fission develop resistant coverings to produce spores. The process is called sporulation. (iii) Budding: Some unicellular organisms such as yeast can put out small buds that separate and grow further. The mode of reproduction in multicellular organisms (i) Fragmentation: Simple multicellular organisms such as spirogyra simply break up into smaller pieces upon maturation. These pieces, known as fragments, grow into new individuals. (ii) Regeneration: In some fully differentiated organisms—an individual, such as Hydra and Planaria, if somehow cut or broken up into many pieces, many of these pieces grow into separate individuals, Regeneration is carried out by specialised cells. (iii) Budding: Organisms, such as Hydra use regenerative cells for reproduction in the process of budding. In Hydra, an outgrowth, called bud, develops at a specific site. When there buds mature, they detach from the parent body and become new independent individuals. (iv) Sexual reproduction: This mode of reproduction is common in complex multicellular organisms. In this mode of sexual reproduction, both sexes—males and females—are needed to produce new generation. Thus, sexual mode of reproduction involves two individuals. 21. What could be the reasons for adopting contraceptive methods? Ans. Reasons for adopting contraceptive methods (i) The sexual act always has the potential to lead to pregnancy. If woman (mother) is not in good health or mentally not prepared, it will cause adverse effect on the mother and the foetus. (ii) There are many diseases such as AIDS, gonorrhoea, syphilis which are transmitted through sexual act. These can be prevented by the use of contraceptives. (iii) Reproduction process causes increase in population, if adequate measures are not taken to prevent pregnancy. The increase in population in our country is increasing exponentially. This put strains on the natural resources of the country and is a major cause of poverty in our country. Thus, adopting contraceptive can prevent: (i) unwanted pregnancies. (ii) spread of sexually transmitted diseases (STDs) and lethal diseases like AIDS and HIV. (iii) frequent pregnancies which may cause health hazards to mother and her infant. 22. Why are budding, fragmentation and regeneration all considered as asexual types of reproduction? With neat diagrams explain the process of regeneration in Planaria. Ans. Budding, fragmentation and regeneration are considered as asexual types of reproduction because all of them involve only one parent and gametes are not involved in reproduction. No fertilisation and then zygote formation occur in asexual reproduction.

How do Organisms Reproduce? 63 Regeneration in Planaria 23. Write two points of difference between asexual and sexual types of reproduction. Describe why variations are observed in the offspring formed by sexual reproduction. Ans. Asexual reproduction Sexual reproduction (a) Involves only one parent (a) Often involves two parents (b) Gametes are not produced (b) Gametes are produced (c) Fertilisation and zygote formation (c) Fertilisation and zygote formation are are not observed observed (d) Meiosis does not occur at anytime (d) Meiosis occurs at the time of gamete during reproduction formation During sexual reproduction two types of gametes fuse. Although the gametes contain the same number of chromosomes, their DNA is not identical. This situation generates variations among the offsprings. 24. Distinguish between pollination and fertilisation. Mention the site and product of fertilisation in a flower. Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule. Ans. The process or mechanism of transfer of pollen grains from the anther to the stigma is termed as pollination. Pollen grain Stigma Male gamete Pollen tube Ovary Ovule Egg Pollen tube growth and its entry into the ovule

138 Science–X Ans. (i) P is south pole and Q is north pole. (ii) Yes, the magnetic field lines are closed. (iii) (a) By increasing the current flowing. (b) By increasing the number of turns of the solenoid. 50. The substances which have the property of attracting small pieces of iron, nickel, cobalt, etc. are called magnets. Pieces of iron and other magnetic materials can be made to acquire the properties of natural magnets. (a) What is the origin of the word magnetism? (b) Give two properties of magnets. Ans. (a) The word magnetism derived its name from the place Magnesia where the natural magnets were first found. (b) Magnets have both attractive and directive properties. 51. A magnet produces a magnetic field in the space around it, which exerts a force on any other magnet placed in it. Field lines are used to represent a magnetic field. A field line is the path along which a hypothetical free north pole would tend to move. The direction of the magnetic field at a point is given by the direction that a north pole placed at that point would take. Field lines are shown closer where the magnetic field is greater. (a) What is a magnetic field line? (b) Can two magnetic field lines intersect? Justify. (c) Give two properties of magnetic field lines. Ans. (a) A magnetic field line may be defined as the curve the tangent to which at any point gives the direction of the magnetic field of that point. (b) No. If two magnetic field lines intersect, then there will be two tangents and hence two directions of magnetic field at the point of intersection which is not possible. (c) (i) The magnetic field lines are closed curves which start in air from N-pole and end at the S-pole and then return to the N-pole through the interior of the magnet. (ii) Field lines are closer together in the regions of strong field and farther apart in the regions of weak field. 52. A student performs an experiment to study the magnetic effects of current around a current carrying conductor. He reports that the direction of the north pole of a compass needle kept at a given point near the conductor gets reversed when the terminals of the battery are interchanged. (a) What is the nature of magnetic field of a straight current carrying conductor? (b) Name and state a rule for finding the direction of this field. (c) Give two factors on which magnitude of field depends. Ans. (a) Magnetic field are concentric circles with their centres of wire. (b) Right-hand thumb rule. (c) (i) Current through conductor (ii) Distance from the conductor

Magnetic Effects of Current 139 3. LONG ANSWER TYPE QUESTIONS [5 Marks] 1. Figure shows a closed coil connected to a galvanometer G. The galvanometer shows a deflection to the right when N-pole of the bar magnet is brought closer to the coil AB. (i) Why does the deflection occur in the A B galvanometer? S N (ii) State the observation when (a) the coil is moved away from N- pole. G (b) both the coil and magnet are moved to the right with the same speed. (CBSE 2016) Ans. (i) As the magnet is moved closer to coil AB, the flux linked with the coil increases. This sets up induced current in the coil as shown by deflection in the galvanometer. (ii) (a) The direction of induced current in the soil AB is reversed and the galvanometer shows a deflection to the left. (b) When both the magnet and the coil AB are moved towards right with the same speed, the flux linked with the coil does not change. No induced current is set up. Hence no deflection is shown by the galvanometer. 2. A coil made of insulated copper wire is connected to a galvanometer. (i) What will happen to the deflection of the galvanometer if this coil is moved towards a stationary bar magnet and then moved away from it? (ii) Give reason for your answer and name the phenomenon involved. (CBSE 2015) Ans. (i) When the coil is moved towards the bar magnet, the galvanometer shows deflection in one direction. Reason: When the coil is moved towards the stationary bar magnet, the magnetic flux linked with it increases and a current is induced in it, as is shown by deflection in the galvanometer. (ii) When the coil is moved away from the coil, the galvanometer shows deflection in opposite direction. Reason: When the coils is moved away from the magnet, the magnetic flux linked with it decreases and a current is induced in the coil in the opposite direction, as shown by deflection in the galvanometer in opposite direction. This phenomenon is called electromagnetic induction. 3. Draw the magnetic field lines of the field produced by a current carrying circular loop. Explain with reason whether the field will be stronger at a point at the centre of loop or near the circumference of N S loop. (CBSE 2015) Ans. Magnetic field due to a current through a circular – loop: The given figure shows the magnetic field + lines of a circular wire carrying a current. The lines of force near the wire are almost concentric circles.

140 Science–X As we move towards the centre of loop, the concentric circles become larger and larger. Near the centre of the loop, the arcs of these big circles appear as parallel straight lines. Thus the magnetic field is almost uniform at the centre of the loop. By applying right-hand rule, we can see that the magnetic field lines due to all sections of the wire are in the same direction within the loop. That is why the field is stronger at the centre or near the circumference of the loop. 4. (a) Name two electrical appliances of daily use in which electric motor is used. (b) Name and state the principle on which an electric motor works. (CBSE 2014) Ans. (a) Electric motor is commonly used in fan, washing machine, mixer, etc. (b) An electric motor works on the Fleming’s left-hand rule. Motion of Field conductor Magnetic field Current Force Current Fleming’s left-hand rule: When we stretch our thumb, forefinger and middle finger so that they are mutually perpendicular to one another, the forefinger points in the direction of the magnetic field and the middle finger points in the direction of the current; the thumb gives the direction of the force acting on the conductor. 5. What is an electromagnet? What decides its polarity? How it differs from a permanent magnet? List the three factors and explain how strength of an electromagnet depends on these. (CBSE 2014) Ans. • When a soft iron is placed inside a solenoid and current is passed through it, then the soft iron gets magnetised. The magnet so formed is called an electromagnet. • Its polarity is decided by the direction of current flowing through the solenoid. • Permanent magnets have constant magnetic field around them whereas magnetic field of electromagnet is temporary. • Strength of an electromagnet depends on: (i) The number of turns in the solenoid. (ii) Strength of current flowing through the solenoid. (iii) Position of soft iron core within the solenoid. 6. (a) Draw magnetic field lines of a bar magnet. “Two magnetic field lines never intersect each other”. Why? (b) An electric oven of 1.5 kW is operated in a domestic circuit (220 V) that has a current rating of 5 A. What result do you expect in this case? Explain. (CBSE 2013, 2014) Ans. (a) Magnetic field lines around a bar magnet. If two magnetic field lines intersect at a point, then at the point of intersection, there must be two direction of the same field, which is not possible.

Magnetic Effects of Current 141 (b) Here, P = 1.5 kW = 1500 W ∴ Current I = P = 1500 ∼7A V 220 Thus, the current flowing through the circuit when oven is ON is nearly 7 A which is higher than the current rating (5 A) of the circuit. ∴ The wiring of the circuit may burn, fuse wire will also blow off breaking the circuit and stopping the current supply. 7. (a) Explain any three properties of magnetic field lines. (b) Give two uses of magnetic compass. (CBSE 2013) Ans. (a) (i) Field lines emerge from north pole and merge at south pole outside the magnet. (ii) They are closed curves. (iii) Magnetic force is greater where the field lines are crowded. (iv) No two field lines are found to cross each other. (b) Uses of magnetic compass: (i) A magnetic compass can be used to find direction. (ii) It can be used to test if a substance has magnetic properties. 8. (a) State Fleming’s left hand rule. (b) Write the principle of working of an electric motor. (c) Explain the function of the following parts of an electric motor: (i) Armature (ii) Brushes (iii) Split ring (CBSE 2018) Ans. (a) Fleming’s Left-Hand Rule: Stretch the first three fingers of the left hand mutually perpendicular to each other such that the forefinger points the direction of magnetic field, the middle finger points the direction of current, then the thumb will indicate the direction of force experienced by the conductor. Fig. Fleming’s left-hand rule (b) Principle of Working of an Electric Motor: When a conductor is placed in a magnetic field and current is passed through it, a force acts on the conductor which rotates it continuously. (c) (i) When current passes through the armature placed between two poles of the horse-shoe magnet, it experiences a force and starts rotating which in turn

142 Science–X rotates the shaft of the electric motor which is supported by a pulley. By using a conveyor belt on pulley, the rotating part of other devices such as grinding mill etc. can be made functional. (ii) The function of carbon brushes is to make contact with the rotating rings of the commutator and through them to supply current to the armature. (iii) The split rings reverse the direction of current flowing through the armature after every half rotation of the coil (armature). 10. Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor? Ans. An electric motor is a rotating device which converts electrical energy into mechanical energy. Principle: An electric motor works on the principle that a current carrying conductor placed in a magnetic field experiences a force, the direction of force is given by Fleming’s left-hand rule. Construction: As shown in the given figure, an electric motor consists of the following main parts: (i) Field magnet: It is a strong horse-shoe type magnet with concave poles. (ii) Armature: It is a rectangular coil ABCD having a large number of turns of thin insulated copper wire wound over a soft iron core. (iii) Split ring commutator: It consists of a cylindrical metal ring split into two halves S1 and S2. The two ends A and D of the armature coil are connected to the split rings S1 and S2 respectively. (iv) Brushes: Two graphite or flexible metal rods maintain a sliding contact with split rings S1 and S2, alternately. (v) Battery: A battery of few cells is connected to the brushes. The current from the battery flows to the armature coil through the brushes and the split rings. Direction of rotation Armature coil B C F NA F Field magnet DS Brush B1 S1 Split ring S2 B2 Plug-key +– Battery An electric DC motor

Magnetic Effects of Current 143 Working: Initially, suppose the plane of the coil is horizontal. The split ring S1 touches the brush B1 and split ring S2 touches the brush B2. The current in coil flows in the direction ABCD, as shown in the figure. The currents in arms AB and CD are in opposite directions. The magnetic force acting on arm AB pushes it downwards while the force acting on the arm CD pushes it upwards. Thus, the armature coil along with the axle rotates anticlockwise. After half a rotation, the split ring S1 comes in contact with brush B2 and S2 in contact with brush B1. Therefore, the current flows along the path DCBA. Thus, the arm AB is now pushed up and the arm CD is pushed down. Therefore, the coil and the axle rotate half a turn more in the same direction. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil and to the axle. The function of the split ring commutator is to reverse the direction of current in the armature coil after every half rotation. 11. Why does a magnetic compass needle pointing North and South in the absence of a nearby magnet get deflected when a bar magnet or a current carrying loop is brought near it? Describe some salient features of magnetic lines of field concept. Ans. Current carrying loops behave like bar magnets and both have their associated lines of field. This modifies the already existing earth’s magnetic field and a deflection results. Magnetic field has both direction and magnitude. Magnetic field lines emerge from N-pole and enter S-pole. The magnetic field strength is represented diagrammatically by the degree of closeness of the field lines. Field lines cannot cross each other as two values of net field at a single point cannot exist. Only one value, a unique net value, can exist. If in a given region, lines of field are shown to be parallel and equispaced, the field is understood to be uniform. 12. With the help of a labelled circuit diagram illustrate P –+ the pattern of field lines of the magnetic field around A a current carrying straight long conducting wire. How + is the right-hand thumb rule useful to find direction – of magnetic field associated with a current carrying conductor? Ans. Right-hand thumb rule states that if a current K carrying straight conductor is supposedly held in the right hand with the thumb pointing towards the direction of current, then the fingers will wrap around the conductor in the direction of the field lines of the magnetic field. 13. Explain with the help of a labelled diagram the N S distribution of magnetic field due to a current through a circular loop. Why is it that if a current carrying coil has n turns, the field produced at any point is n times as large as that produced by a single turn? Ans. The magnetic field (B) produced by current – carrying circular wire depend on: + (i) Amount of current flowing through wire (I): B∝I Magnetic force (lines) due to current carrying through a loop

144 Science–X (ii) Number of turns on the circular wire (N) BN If there is a circular coil having N turns, the field produced is N times as large as that produced by a single turn. 14. Describe the activity that shows that a current-carrying conductor experiences a force perpendicular to its length and the external magnetic field. How does Fleming’s left- hand rule help us to find the direction of the force acting on the current carrying conductor? Ans. Aim: To show that force is exerted on a current carrying conductor placed in a strong magnetic field. Materials required: A conducting rod (AB), connecting wires, horse- shoe magnet, battery switch and clamp stand. Procedure: (i) Connect the conducting rod (AB) to the battery and key. (ii) Place a strong horse-shoe magnet in such a way that the rod AB lines between the poles with magnetic field directed upwards i.e. N. Pole is vertically above the rod. (iii) Plug in the key. Observation: A current-carrying rod AB experiences a force perpendicular to its length and the magnetic field. According to Fleming’s left-hand rule, stretch the thumb, the forefinger and the middle finger of your left hand such that they are mutually perpendicular. If the fore-finger points in the direction of magnetic field and the middle in the direction of current, then the thumb will point in the direction of motion or force acting on the conductor. 15. Draw a labelled circuit diagram of a simple electric motor and explain its working. In what way these simple electric motors are different from commercial motors? Ans. The circuit diagram of a simple electric motor is shown below. Working: (i) Let coil ABCD be in horizontal position. When the key is switched on, the current flows in direction DCBA and then leaves through the brushes B2 via ring R2. (ii) Applying Fleming’s left hand rule, no force acts on arm BC and AD as they are parallel to magnetic field, arm AB experiences a force in downward direction and arm CD experiences an equal force in upward direction. A torque acts on the coil and it rotates in anti-clockwise direction. (iii) While rotating, the coil reaches the vertical position, brushes loose contact with the rings and current stops flowing. But the coil does not stop due to inertia of motion.

Magnetic Effects of Current 145 B C NS P AD Split rings Y (P and Q) Brushes (X and Y) X + –K Simple electric motor (iv) When the coil passes the vertical position, the rings automatically change their positions and come in contact with opposite brushes. (v) This reverses the direction of current through the coil but the direction of current on right hand side remains same. (vi) So, the force on right hand side is always upward and a force on left hand side is always in downward direction. Thus, the coil continues to anti-clockwise direction. A commercial electric motor is one which uses the following: (i) An electromagnet in place of permanent magnet. (ii) Large number of turns of conducting wire in current carrying coil. (iii) A soft iron core on which the coil is wound. The combination of soft iron core and coil is an armature. It enhances the power of motor. Thus, commercial electric motors do not use permanent magnet to rotate the armature because permanent magnets are weak and do not produce strong magnetic field in the region. 16. Explain the phenomenon of electromagnetic induction. Describe an experiment to show that a current is set up in a closed loop when an external magnetic field passing through the loop increases or decreases. Ans. This phenomenon was discovered by Michael Faraday and Joseph Henry in 1831. The phenomenon of generation of an electric current in a closed circuit from magnetic effects i.e., by changing the magnetic field is called electromagnetic induction. Electric current produced due to this phenomenon is called induced current. The potential difference set in the circuit due to induced current is called induced emf. Experiment: Let two different coils of copper wire, namely coil 1 and coil 2, having large number of turns are arranged as per the circuit diagram as shown in figure. The coil 1, having larger number of turns, is connected in series with a battery and a plug key whereas the other coil 2 is connected with a galvanometer as shown in circuit

146 Science–X diagram. When key K is closed, the galvanometer shows a deflection in its needle instantly jumps to one side and just as quickly returns to zero, indicating a momentary current in coil 2. This happens due to an external magnetic field passing through the loop increases. When key K is open, the coil 1 is disconnected from the battery. The needle momentarily moves, but to the opposite side. It means that now the current flows in the opposite direction in coil 2. This happens due to an external magnetic field passing through the loop decreases. 4. CASE STUDIES Read the passages carefully answer the questions that follow. 1. The current produced in the coil by changing magnetic flux linked with it is called the induced current and the corresponding potential difference is called the induced potential difference or induced electromotive force (emf). The phenomenon is called the electromagnetic induction. It is important to note that the induced current (or induced potential difference) is not like the one due to an electric cell. In an electric cell, it is the chemical energy that is converted into electric energy (i.e., current). In case of electromagnetic induction, the induced current is due to changing magnetic flux in the coil. Since to change magnetic flux, we have to do work to cause relative motion between the magnet and the coil, it is this work (i.e., mechanical energy) that is converted into electric energy. Answer the following questions: (i) The magnetic effect of current was discovered by (a) Faraday (b) Henry (c) Oersted (d) Maxwell (ii) Electromagnetic induction is involved in (a) charging a body with positive charge (b) production of current by relative motion between magnet and the coil (c) rotation of the coil of an electric motor (d) generation of magnetic field due to a current carrying solenoid. (iii) A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each (a) two revolution (b) one revolution (c) half revolution (d) one-fourth revolution (iv) If V be the change in potential between two neighbouring points r apart, then the magnitude of electric field E is given by (a) E = ΔV × Δr (b) E= ΔV Δr (c) E= Δr (d) E = (ΔV)2 ΔV Δr 2. The iron filings arrange themselves in a pattern as shown in the given figure. The magnet exerts its influence in the region surrounding it. Therefore, the iron filings experience a force. The force thus exerted makes iron filings to arrange in a definite

Magnetic Effects of Current 147 pattern. The region surrounding a magnet, in which the force of the magnet can be detected, is said to have a magnetic field. The lines along which the iron filings align themselves represent magnetic field lines. NS Answer the following questions: (i) The scientist who discovered the magnetism produced due to current carrying conductor was (a) Oersted (b) Maxwell (c) Faraday (d) Ohm (ii) Choose the correct statement: (a) Lines of force are not imaginary lines. (b) Lines of force cannot be mapped on paper. (c) Lines of force do not intersect each other. (d) Lines of force always intersect each other. (iii) Which of the following figures represents the magnetic lines of force due to an isolated south pole? (a) (b) (c) (d) (iv) An electron is circulating in a plane at right angle to a uniform magnetic field B = 1 × 10–4 T. The velocity of electron is given as 1.9 × 106 ms–1. The orbital radius of it will be (a) ∼ 0.18 m (b) ∼ 0.16 m (c) ∼ 0.14 m (d) ∼ 0.11 m 3. The pattern of the magnetic field lines around a carrying solenoid is shown in figure. This pattern similar to the magnetic field around a bar magnet. End of the solenoid

148 Science–X behaves as a magnetic north the other behaves as the south pole. The field the solenoid are in the form of parallel straight indicates that the magnetic field is the same at all the solenoid. That is, the field is uniform inside. A strong magnetic field produced inside be used to magnetise a piece of magnetic material, like soft iron, when placed inside the coil. The magnet so formed is called an electromagnet. +– K Answer the following questions: (i) By increasing number of turns in the coil, the strength of the magnetic field (a) decreases (b) increases (c) first increases then decreases (d) remains unchanged (ii) By inserting a soft iron piece into a solenoid, the strength of the magnetic field (a) increases (b) decreases (c) first increases then decreases (d) remains unchanged (iii) For making electromagnet, core of which material will you prefer (a) soft iron (b) hard steel (c) carbon steel (d) chromium steel (iv) In the arrangement shown in figure below here are two coils wound on a non- conducting cylindrical rod. Initially the key is not inserted. Then the key is inserted and later removed. Then +– (a) the deflection in the galvanometer remains zero throughout (b) there is a monetary deflection in the galvanometer but it dies out shortly and there is no effect when the key is removed (c) there are momentary galvanometer deflections that die out shortly; the deflections are in the same direction (d) there are momentary galvanometer deflections that die out shortly; the deflections are in opposite directions

Magnetic Effects of Current 149 4. If the current (I) in the conductor PQ increased, the deflection of the needle of the compass (used for mapping the field) also increases. Since deflection of the compass is a measure of B, it is clear that magnetic field (B) increases with the increase in current (I), i.e., B∝I ...(i) Straight conductor If the distance (r) of the compass from the conductor is increased, the deflection of the needle decreases, i.e., B∝ 1 ...(ii) r Combining (i) and (ii), we get B∝ 1 ...(iii) r Answer the following questions: (i) The magnetic lines of force of a straight conductor carrying current are (a) parallel to conductor (b) concentric circles (c) perpendicular to conductor (d) both (b) and (c) (ii) A wire 10 cm long and carrying a current of 1.5 A is held in a uniform magnetic field in which B = 10–3 T. The force on the wire if it is held perpendicular to the lines of the magnetic field will be (a) 10 × 10–5 N (b) 10.5 × 10–5 N (c) 15 × 10–5 N (d) 15.5 × 10–5 N (iii) Fleming’s right hand rule gives (a) the magnitude of the induced e.m.f (b) the magnitude of the magnetic field. (c) the direction of the induced e.m.f. (d) both magnitude and direction of the induced e.m.f.

150 Science–X (iv) The relation between weber and tesla is (a) 1 Wb = 1 T (b) 1 Wb = 1 T × 1 m2 (c) 1 Wb = 1 T × 1 m–2 (d) 1 Wb2 = 1 T × 1 m2 5. Faraday, on the basis of his experiments, formulated the following two laws of electromagnetic induction. (a) Whenever there is a change in magnetic flux linked with a coil , an electric current (and pd) is induced. This induced pd lasts so long as there is a change in the magnetic flux linked with the coil. (b) The magnitude of the induced current (and pd) is directly proportional to the rate of change of magnetic flux linked with the coil. If the rate of change of magnetic flux remains uniform, a steady pd is induced. If the circuit of the coil is closed, a current flows in the coil due to induced pd at its ends. It is clear that the magnitude of induced pd depend on: (i) the change in magnetic flux and (ii) the time in which flux changes. Thus, (i) more the change in magnetic flux, more is the induced pd and (ii) Faster the change in magnetic flux, more is the induced pd. Answer the following questions: (i) A current is flowing in a circular loop of wire in clockwise direction. The magnetic field at the centre of the loop is (a) directed downward (b) zero (c) inversely proportional to the radius of the loop (d) both (a) and (c) (ii) Current carrying conductor placed in a magnetic field experiences a force. The device is based on this principle is (a) electric generator (b) electric motor (c) electric bell (d) none of these (iii) A copper ring is moved towards the north pole of a bar magnet. Then (a) the ring will not be affected (b) the ring all tend to get warm (c) alternating current will flow in the ring (d) the ring will be positively charged (iv) Which among the following is true about Faraday’s law of induction? (a) An e.m.f. is induced in a conductor when it cuts the magnetic flux (b) An e.m.f. is induced in a conductor when it moves parallel to the magnetic field (c) An e.m.f. is induced in a conductor when it moves perpendicular to the magnetic field (d) An e.m.f. is induced in a conductor when it is just entering a magnetic field. Answers 1. (i) (c) Oersted (ii) (b) production of current by relative motion between magnet and the coil

Magnetic Effects of Current 151 (iii) (c) half revolution (iv) (b) E= ΔV Δr 2. (i) (a) Oersted (ii) (c) Lines of force do not intersect each other (iii) (a) (iv) (d) Hint: The force experienced by the electron is given by Bev, and it provides the necessary centripetal force. ∴ mv2 = Bev r or r= mv ...(i) Be Taking the standard values of m and e for an electron, we have m = 9.10 × 10–31 kg and e = 1.6 × 10–19 C. Putting these values of in equation (i) we get r= 9.1 × 10−31 × 1.9 × 106 ∼ 0.11 m 1 × 10−4 × 1.6 × 10−19 3. (i) (b) increases (ii) (a) increases (iii) (a) soft iron (iv) (d) there are momentary galvanometer deflections that die out shortly; the de- flections are in opposite directions. 4. (i) (d) both (b) and (c) (ii) (c) Hint: l = 10 cm = 0.10 m, I = 1.5 A, B = 10–3 T F = Bil = 10–3 × 1.5 × 0.1 = 15 × 10–5 N (iii) (c) the direction of the induced e.m.f. (iv) (b) 1 Wb = 1 T × 1 m2 5. (i) (d) both (a) and (c) (ii) (b) electric motor (iii) (b) Hint: The ring all tend to get warm, because when the copper ring is moved towards the north pole of the magnet, induced e.m.f. is generated in the ring according to the electromagnetic laws of induction. Now current in the ring due to induced e.m.f. will generate heat in the ring according to Joule’s law. Thus, the copper ring tends to get warm. (iv) (a) Hint: According the Faraday’s law of electromagnetic induction, an e.m.f. is induced in a conductor when it cuts across the flux of a magnetic field. If the two ends of the conductor are connected to an outside circuit the induced e.m.f. causes current to flow in the circuit.

ISBN: 978-93-93268-96-9 789393 268969 T10-0959-249-COMP.CBSE QB SCIENCE T-II X