physics part 1

ALLENÒ CBSE 145 11. (a)Define mutual inductance between a pair of coils. Derive an expression for the mutual inductance of two long coaxial solenoids of same length wound one over the other. (b)A thin iron sheet is placed between two coils, other factors remaining the same. Explain answer in each case. [5] 12. Mutual inductance is the phenomenon of inducing emf in a coil, due to a change of current in the neighboring coil. The amount of mutual inductance that links one coil to another depends very much on the relative positioning of the two coils, their geometry and relative separation between them. Mutual inductance between the two coils increases Uptimes if the coils are wound over an iron core of relative permeability µr. node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 05_Unit-4.docx(i) A short solenoid of radius a, number of turns per unit length n1 and length L is kept coaxially inside a very long solenoid of radius b, number of turns per unit length n2. www.notesdrive.comWhat is the mutual inductance of the system? (A) µopb2n1n2L (B) µopa2n1n2L2 (C) µopa2n1n2L (D) µopb2n1n2L2 (ii) If a change in current of 0.01 A in one coil produces a change in magnetic flux of 2 × 10–2 Weber in another coil, then the mutual inductance between coils is (A) 0 (B) 0.5 H (C) 2 H (D) 3 H (iii) Mutual inductance of two coils can be increased by :- (A) Decreasing the number of turns in the coils (B) Increasing the number of turns in the coils (C) Winding the coils on wooden cores (D) None of these (iv) When a sheet of iron is placed in between the two co-axial coils, then the mutual inductance between the coils will :- (A) Increases (B) Decreases (C) Remain same (D) Cannot be predicted E

146 Physics ALLENÒ EXERCISE - VI (MOCK TEST) CHAPTER-7 : ALTERNATING CURRENT 1. How much average power over a complete cycle, does an AC supply to a capacitor ? [1] 2. Which is more dangerous 220 V AC or 220V DC. [1] 3. If the peak value of e.m.f. of the source is 200V, find the rms value of emf. [1] 4. An alternating voltage of frequency 'f ' is applied across a series LCR circuit. Let for be the resonance frequency for the circuit. Will the current in the circuit lag, lead or remain in phase with the applied voltage when (i) f > f0 (ii) f < f0 ? Explain your answer. [2] 2. Define the term ‘power loss’ in a conductor of resistance R carrying a current I. In what form does this power loss appear ? Show that to minimise the power loss in the transmission cables connecting the power stations to homes, they carry high values of voltage. [2] www.notesdrive.com 6. A coil of inductance L, a capacitor of capacitance C and a resistor of resistance R are all put in node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 05_Unit-4.docx series with an alternating source of emf E = (E0 sin wt). Write an expression for the [2] (1) Total impedance of the circuit (2) Frequency of the source emf for which the current carrying circuit will show resonance. 7. (i) Define mutual inductance. (ii) A pair of adjacent coils has a mutual inductance of 1.5 H. If the current in one coil changes from 0 to 20A in 0.5 s, what is the change of flux linkage with the other coil? [2] 8. (i) When an AC source is connected to an ideal inductor show that the average power supplied by the source over a complete cycle is zero. (ii) A lamp is connected in series with an inductor and an AC source. What happens to the brightness of the lamp when the key is plugged in and an iron rod is inserted inside the inductor ? Explain. [3] lamp () ~ 9. A capacitor of unknown capacitance, a resistor of 100 W and an inductor of self inductance L = (4/p2) henry are connected in series to an ac source of 200 V and 50 Hz. Calculate the value of the capacitance and impedance of the circuit when the current is in phase with the voltage. Calculate the power dissipated in the circuit. [3] 10. Distinguish between resistances, reactance and impedance of an a.c. circuit? [3] 11. (i) Draw a labelled diagram of a step-down transformer. State the principle of its working (ii) Express the turn ratio in terms of voltages. (iii) Find the ratio of primary and secondary currents in terms of turn ratio in an ideal transformer. (iv) How much current is drawn by the primary of a transformer connected to 220 V supply when it delivers power to a 110 V – 550 W refrigerator ? [5] E

ALLENÒ CBSE 147 12. When a pure resistance R, pure inductor L and an ideal capacitor of capacitance C is connected in series to a source of alternating e.m.f., then current at any instant through the three elements has the same amplitude and is represented as 1 = Iosinwt. However, voltage across each element has a different phase relationship with the current as shown in graph. The effective resistance of RLC circuit is called impedance (Z) of the circuit and the voltage leads the current by a phase angle f. node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 05_Unit-4.docx www.notesdrive.com A resistor of 12W a capacitor of reactance 14W and a pure inductor of inductance 0.1 H are joined in series and placed across 200 V, 50 Hz a.c. supply (i) The value of inductive reactance is (A) 15 W (B) 31.4 W (C) 20 W (D) 30 W (ii) The value of impedance is :- (A) 20 W (B) 15 W (C) 30 W (D) 21.13 W (iii) What is the value of current in the circuit ? (A) 5 A (B) 15 A (C) 10 A (D) 9.46A (iv) What is the value of the phase angle between current and voltage? (A) tan–1 (1.45) (B) tan–1(1.60) (C) tan–1 (1.25) (D) tan–1 (1.75) E

148 Physics ALLENÒ IMPORTANT NOTES ______________________________________________________________________www.notesdrive.com ______________________________________________________________________ ______________________________________________________________________ node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 05_Unit-4.docx ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ E

ALLENÒ CBSE 149 UNIT-V : ELECTROMAGNETIC WAVES (EMW) CHAPTER- 8 : ELECTROMAGNETIC WAVES (EMW) ELECTROMAGNETIC WAVES \"The electromagnetic waves are those waves in which there are sinusoidal variations of electric and magnetic field vectors to right angles to each other as well as at right angles to the direction of wave propagation.\" (i.e., electric and magnetic fields vary with space and time). y node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 06_Unit-5.docxc x z www.notesdrive.com An accelerating charge produces electromagnetic waves. An electric charge oscillating harmonically with certain frequency, produces electromagnetic waves of the same frequency. An electric dipole is a basic source of electromagnetic waves. Electromagnetic waves carry energy as they travel through space and this energy is shared equally by the electric and magnetic fields. Electromagnetic waves transport momentum as well. When these waves strike a surface, a pressure is exerted on the surface. If total energy transferred to a surface in time t is U, total momentum delivered to this surface is p = U/c. MATHEMATICAL REPRESENTATION OF ELECTROMAGNETIC WAVES Electric and magnetic fields oscillate sinusoidally in space and time in an electromagnetic wave. The oscillating electric and magnetic fields, E and B are perpendicular to each other, and to the direction of propagation of the electromagnetic wave. For a wave of frequency n, wavelength l, propagating along x-direction, we have E = Ey(t) = E0 sin (kx - wt) = E0 sin êéë2p æ x - nt öù = E0s in éêë2p æ x - t öù èç l ø÷úû çè l T ø÷úû B = Bz(t) = B0 sin (kx - wt) = B0 sin êéë2p æ x - nt öù = B0s in êëé2p æ x - t öù çè l ÷øûú èç l T ø÷úû These are related by E0 =c B0 E

150 Physics ALLENÒ The speed c of electromagnetic wave in vacuum is related to m0 and e0 (the free space permeability & permittivity constants) c = 1 . m0e0 Electromagnetic waves other than light also have the same velocity c in free space. The speed in a material medium is given by v = 1 where m is the permeability of the medium and e its me permittivity. ENERGY DENSITY OF ELECTROMAGNETIC WAVES We know that, in free space energy density of em waves have energy density of electric field and magnetic field. i.e. u = uE + uB www.notesdrive.comu=12e0Er2ms+B2 rms node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 06_Unit-5.docx 2m0 But Brms = E rms c u =12 e0Er2ms + E2 But c = 1 rms m0e0 2m0c2 u =12 e0Er2ms + E2rmsm0e0 Þ u =12 e 0 E 2 + 1 e 0 E 2 2m0 rms 2 rms u =e0Er2ms Similarly u = B2 rms m0 CHARACTERISTICS OF ELECTROMAGNETIC WAVES 1. The electromagnetic waves travel in free space with the speed of light (3 × 108 m/s) irrespective of their wavelength. 2. The electromagnetic waves are neutral. (These are not deflected by electric and magnetic fields) 3. The electromagnetic waves show properties of reflection, refraction, interference, diffraction and polarization. 4. The ratio of magnitudes of electric and magnetic field vectors in free space is constant equal to c i.e. 3 × 108 m/s 5. The speed of electromagnetic waves in a material medium is v = (me)–1/2 6. In an electromagnetic wave, the energy is propagated by means of electric and magnetic field vectors in the direction of propagation of wave and electric energy density is equal to the magnetic energy density. 7. These are transverse in nature .i.e. in an electromagnetic wave, the field vectors are perpendicular to the direction of propagation of wave. Direction of Electromagnetic Waves: - The direction of electromagnetic waves ( ˆi ) is perpendicular to the plane containing the direction of electric and magnetic vector. ˆi =Er ´ Br E

ALLENÒ CBSE 151 CLASSIFICATION OF ELECTROMAGNETIC WAVES The classification of electromagnetic waves according to their wavelength or frequency is called the electromagnetic spectrum. 1. Radio waves :- These are the e.m. waves of longest wavelength and minimum frequency. Wavelength range - 600 m to 0.1 m Frequency range - 500 kHz to 1000 MHz source - Accelerated motion of charges in conducting wires or oscillating circuits. Properties - Reflection, diffraction. Uses of radio waves: 1. In radio and television communication systems. 2. In radio astronomy. Table- Some important wireless communication bands node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 06_Unit-5.docx Frequency band Service www.notesdrive.com 540-1600 kHz Medium wave AM band 3-30 MHz Shortwave AM band 88-108 MHz FM broadcast 54-890 MHz TV Waves 840-935 MHz Cellular Mobile radio 2. Microwaves :- They are the e.m. waves having wavelengths next smaller to radio waves. Wavelength range: 0.3 m to 10–3 m Frequency range : 109 Hz to 1012 Hz Source: Oscillating currents in special vacuum tubes like klystrons, magnetrons and Gunn diodes. Properties : Reflection, refraction, diffraction and polarization. Due to their shorter wavelengths, they can travel as a beam in a signal. Uses of Microwaves:- 1. In radar systems for aircraft navigation. 2. In long distance communication systems via geostationary satellites. 3. In microwave ovens. 3. Infrared waves- These radiations lie close to the low frequency or long wavelength of the visible spectrum. Infrared waves produce heating effect, so they are also known as heat waves or thermal radiation. The water molecules (and also CO2, NH3 molecules) present in different materials readily absorb infrared waves, increase the thermal motions and hence heat up the materials and their surroundings. Wavelength range - 5 × 10–3 m to 10–6 m Frequency range - 1011 Hz to 5 × 1014 Hz Source- Hot bodies and molecules. Properties - Heating effect, reflection, refraction, diffraction and propagation through fog. E

152 Physics ALLENÒ Uses of Infrared waves: 1. In the remote control of a TV or VCR, the keypad of which contains a small infrared transmitter. 2. In green houses to keep the plants warm. 3. In haze photography because infrared waves are less scattered than visible light by atmospheric particles. 4. Infrared lamps in the treatment of muscular complaints. 5. In reading the secret writings on the ancient walls. 6. In knowing the molecular structure. 4. Visible light- It is a very small part of the e.m. spectrum towards which the human retina is sensitive. The visible light emitted or reflected from bodies around us gives information about the world. Wavelength range- 8 × 10–7 m to 4 × 10–7 m Frequency range- 4 × 1014 Hz to 7 × 1014 Hz Source- Radiated by excited atoms in ionized gas and incandescent bodies. Properties- Reflection, refraction, interference, diffraction, polarization, photoelectric effect, photographic action, sensation of sight. www.notesdrive.com Uses of visible light: 1. It provides us the information of the world around us. node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 06_Unit-5.docx 2. It can cause chemical reactions. The approximate wavelength ranges for lights of different colours are as follows. Table: - Visible Spectrum Color Wavelength range Color Wavelength range Violet, indigo Blue 4000-4500 Å Yellow 5700-5900 Å Green 4500-5000 Å Orange 5900-6200 Å 5000-5700 Å Red 6200-7500 Å 5. Ultraviolet light- This region of the e.m. spectrum has wavelengths just shorter than visible light and can be detected just beyond the violet end of the solar spectrum. Wavelength range - 3.5 × 10–7 m to 1.5 × 10–7 m. Frequency range- 1016 Hz to 1017 Hz. Source- High voltage gas discharge tubes, arcs of iron and mercury, the sun. Properties- Effect on photographic plate, fluorescence, ionization, highly energetic, tanning of the human skin. Uses of ultraviolet light: 1. In food preservation. 2. In the study of invisible writings, forged documents and finger prints. 3. In the study of molecular structure. E

ALLENÒ CBSE 153 The ultraviolet light in large quantities has harmful effects on human beings. But fortunately, most of the ultraviolet light coming from the sun is absorbed by the ozone layer in the atmosphere at an altitude of about 40-50 km. node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 06_Unit-5.docx6. X-ray : These e.m. waves have wavelengths just shorter than ultraviolet light. As X-rays can pass through many forms of matter, so they have many useful medical and industrial applications. www.notesdrive.com Wavelength range- 100 Å to 0.1 Å Frequency range- 1018 Hz to 1020 Hz. Source- Sudden deceleration of fast moving electrons by a metal target. Properties- Effect on photographic plate, ionization of gases, photoelectric effect, fluorescence, more energetic than UV rays. Uses of X-rays 1. In medical diagnosis because X-rays can pass through flesh but not through bones. 2. In the study of crystals structure because X-rays can be reflected and diffracted by crystals. 3. In engineering for detecting faults, cracks, flaws and holes in the finished metal products. 4. In detective departments to detect explosives, diamond, gold, etc. in the possessions of smugglers. 5. In radiotherapy to cure untraceable skin diseases and malignant growths. 7. Gamma rays:- These are e.m. radiations of highest frequency range and lowest wavelength range. These are most penetrating e.m. waves. Wavelength range:- 10–14 m to 10–10m Frequency range:- 1018 Hz to 1022 Hz Source:- Radioactive nuclei and nuclear reactions. Co-60 is a pure g-ray source. Properties:- Effect on photographic plate, fluorescence, ionization, diffraction, high penetrating power. Uses of g-ray:- 1. In radiotherapy for the treatment of malignant tumors. 2. In the manufacture of polyethylene from ethylene. 3. To initiate some nuclear reactions. 4. To preserve food stuffs for a long time because soft -ray can kill micro organisms. 5. To study the structure of atomic nuclei. E

154 Physics ALLENÒ EXERCISE-1 One/Two Marks Questions:- 1. Which wave travels with the speed of light - (A) Sound wave (B) Heat wave (C) Shock wave (D) Micro wave Ans. (D) Micro wave 2. A television network uses - (A) Microwaves (B) High Frequency Radio waves (C) Light waves (D) Sound waves Ans. (B) High Frequency Radio waves 3. Light waves are - (A) Longitudinal (B) Transverse www.notesdrive.com (C) Both Longitudinal and transverse (D) Mechanical node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 06_Unit-5.docx Ans. (B) Transverse 4. Intensity of wave is proportional to ..................... Ans. Intensity of wave is proportional to square of it's amplitude. 5. Frequency range of audio signal .................. Ans. Frequency range of audio signal 20 Hz to 20kHz 6. Ultraviolet rays coming from sun are absorbed by ................. part of atmosphere. Ans. Ultraviolet rays coming from sun are absorbed by ionosphere part of atmosphere. 7. Match the column :- Column (A) Column (B) (a) Gamma rays (i) Treatment of muscular strain (b) X-ray (ii) Kill bacteria from water (c) UV (iii) Study of nuclear structure (d) Infrared (iv) Medical Examination (e) Radio waves (v) Communication Ans. Column (A) Column (B) (a) Gamma rays (iii) (i) Treatment of muscular strain (b) X-ray (iv) (ii) Kill bacteria from water (c) UV (ii) (iii) Study of nuclear structure (d) Infrared (i) (iv) Medical Examination (e) Radio waves (v) (v) Communication 8. In which situation is there a displacement current but no conduction current ? Ans. In between the plates of capacitor , during charging and discharging of a capacitor. 9. Why are microwaves considered suitable for radar systems used in aircraft navigation ? Ans. Microwaves have energy more than radio waves , so these can travel up to greater distance. 10. The charging current for a capacitor is 0.25 A. What is the displacement current across its plates? Ans. 0.25 A . E

ALLENÒ CBSE 155 node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 06_Unit-5.docx11. How are infrared waves produced ? Write their one important use. Ans. Infrared waves are produced by hot bodies due to molecular vibrations. www.notesdrive.com These are used to treat muscular strain. 12. The thin Ozone layer on top of the stratosphere is crucial for human survival. Why ? Ans. Ozone layer absorbs harmful ultraviolet radiation . 13. State two properties of electromagnetic waves. Ans. (i) All em waves travel with same speed c = 3 × 108 m/s in air or vacuum. (ii) Em waves have energy and momentum and these apply radiation pressure, on the surface on which these made to fall. 14. How can we show that em waves carry momentum ? Ans. When an em wave interacts with an electron [ as in photoelectric effect ] the electron get disturbed and also get ejected from metal surface , it is because of energy and momentum imparted by em waves. 15. Which component of the electromagnetic wave is responsible for producing optical effect ? Ans. Electric vector of em wave is responsible . 16. Light can travel in vacuum whereas sound cannot do so. Why ? Ans. Light is electromagnetic in nature while sound is mechanical wave. 17. Optical and radio telescopes are built on the ground but X-ray astronomy is possible only from satellites orbiting the earth. Why ? Ans. Our atmosphere is opaque for X- ray , so for X- ray astronomy we have to use space station. 18. It is said that global nuclear war can cause serve \"nuclear winter\" which can finish human life completely. Explain the basis of this prediction. Ans. The thick layer of pollution caused due to nuclear war will cover the whole earth for centuries , which can finish all types of life on earth. 19. Suppose that earth's atmosphere is absent, will the average temperature on earth's surface be higher or lower than what it is at present ? Ans. The average temperature will be lower due to absence of green house effect. 20. What is electromagnetic constant ? Ans. All types of electromagnetic waves move with same speed c = 3 × 108 m/s in air or vacuum , so 'c' is called electromagnetic constant. 21. Which part of electro-magnetic spectrum is used for eye surgery ? Ans. Ultra-violet rays are used in Lasik Laser, for eye surgery. 22. Which part of electromagnetic spectrum is blocked by protective welding glass ? Ans. Ultra-violet. 23. For which wavelength our eyes are most sensitive ? Ans. 555nm i.e. yellow colour. 24. Which of the electro-magnetic wave capable of penetrating layers of dust ? Ans. Infra-red. 25. Write the wavelength used to check metal surface or to study the crystal structure. Ans. X- rays. E

156 Physics ALLENÒ EXERCISE-II ASSERTION AND REASON Directions (Q. Nos. 1-10) In the following questions an Assertion (A) is followed by a corresponding Reason (R). Use the following keys to choose the appropriate answer. (a) Both (A) and (R) are correct, (R) is the correct explanation of (A). (b) Both (A) and (R) are correct, (R) is not the correct explanation of (A). (c) (A) is correct; (R) is incorrect. (d) (A) is incorrect; (R) is incorrect 1. Assertion: electromagnetic waves do not require medium for their propagation. Reason: they cannot travel in a medium. www.notesdrive.com 2. Assertion: A changing electric field produce magnetic field. Reason: a changing magnetic field produced an electric field. node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 06_Unit-5.docx 3. Assertion: X-rays travel with the speed of light. Reason: X -rays are electromagnetic rays. 4. Assertion: Environmental damages has increased amount of ozone in Atmosphere. Reason: increase of ozone increases amount of ultraviolet radiation on the earth. 5. Assertion: Electromagnetic Radiation exerts pressure. Reason: Electromagnetic wave carry both momentum and energy. 6. Assertion: The EM waves of shorter wavelength can travel longer distances than those of longer wavelengths. Reason: Shorter the wavelength, the larger is the velocity of propagation. 7. Assertion: EM waves follow Superposition principle. Reason: Differential expression of EM wave is linear. 8. Assertion: Sound waves cannot travel in vacuum, but light waves can. Reason: Light is an electromagnetic wave - but sound is a mechanical wave. 9. Assertion: The microwaves are better carriers of signals than radio wave. Reason: The electromagnetic waves do not require any medium to propagate. 10. Assertion: Transverse waves are not produced in liquids and gases. Reason: Shorter the wavelength, the larger is the velocity of propagation in air. ANSWER KEY 1. (c) 2. (b) 3. (a) 4. (d) 5. (a) 6. (c) 7. (a) 8. (a) 9. (b) 10. (c) E

ALLENÒ CBSE 157 EXERCISE-III CASE STUDY BASED QUESTIONS GAMMA RAYS IN TREATMENT OF CANCER FIVE MARKS QUESTIONS: 1. Gamma rays are used in radiotherapy to treat cancer. They are used to spot tumors. They kill the living cells and damage malignant tumor. node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 06_Unit-5.docx(i) What is the source of gamma rays? www.notesdrive.com(A) radioactive decay of nucleus (B) accelerated motion of charges in conducting wire (C) hot bodies and molecule (D) klystron valve Ans. (A) (ii) How is wavelength of gamma rays (A) low (B) high (C) infinite (D) zero Ans. (A) (iii) Choose the one with correct penetrating power order of radiation ? (A) alpha > beta > gamma (B) beta > alpha > gamma (C) gamma > beta > alpha (D) gamma > alpha > beta Ans. (C) (iv) What is other use of gamma rays? (A) used to change white topaz to blue topaz (B) used in aircraft navigation (C) used in kill microbes (D) checking fractures of bone Ans. (A) E

158 Physics ALLENÒ 2. X-rays are a form of electromagnetic radiation, similar to visible light. Unlike light, however, x-rays have higher energy and can pass through most objects, including the body. Medical x-rays are used to generate images of tissues and structures inside the body (i) What is the most common method of preparation of X rays ? www.notesdrive.com (A) magnetron valve (B) vibration of atoms and molecules node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 06_Unit-5.docx (C) bombardment of metal by high energy electrons (D) radioactive decay of nucleus Ans. (C) (ii) Which of the following set of instrument /equipment can detect X- rays (A) Photocells, photographic film (B) Thermopiles, bolometer (C) Photographic film, Geiger tube (D) Geiger tube, human eye Ans. (C) (iii) Where do X rays fall on the electromagnetic spectrum? (A) Between UV region and infrared region (B) Between gamma rays and UV region (C) Between infrared and microwaves (D) Between microwaves and radio waves Ans. (B) (iv) What is the use of rays lying beyond X ray region in electromagnetic spectrum (A) used to kill microbes (B) used to detect heat loss in insulated systems (C) used in standard broadcast radio and television (D) used In oncology, to kill cancerous cells. Ans. (D) E

ALLENÒ CBSE 159 EXERCISE - IV (RACE) (1 Marks each) Very short Answer type Questions 1. Name the electromagnetic radiations used for viewing objects through haze and fog. 2. Write the frequency limit of visible range of electromagnetic spectrum in kHz. 3. Write the following radiations in an ascending order in respect of their frequencies: X-rays, microwaves, ultraviolet rays and radio waves. 4. Name the electromagnetic radiations used for studying crystal structure of solids. 5. Why are microwaves used in RADAR? 6. Which part of electromagnetic spectrum has largest penetrating power? 7. Which part of electromagnetic spectrum has highest frequency? 8. What is the ratio of speed of infra-red rays and ultra-violet rays in vacuum? 9. What is the ratio of speed of gamma rays and radio waves in vacuum? 10. Arrange the given electromagnetic radiations in the descending order of their frequencies: Infra-red, X-rays, Ultraviolet and Gamma rays. 11. When can a charge act as a source of electromagnetic waves ? 12. A radio can tune in to any station in the 7.5 MHz to 12 MHz band. What is the corresponding wavelength band? 13. A charged particle oscillates about its mean equilibrium position with a frequency of 109 Hz. What is the frequency of the electromagnetic waves produced by the oscillator? 14. Which part of electromagnetic spectrum does the wavelength 10–10 m corresponds to? 15. What do electromagnetic waves consist of ? Explain on what factor does its velocity in vacuum depend. 16. What is the phase difference between electric and magnetic field vectors ? 17. Give a reason to show that microwaves are better carrier of signal for long range transmission than radio waves. node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 06_Unit-5.docx Short Answer Type Questions-I (2 Marks each) www.notesdrive.com 18. Find the wavelength of electromagnetic waves of frequency 5 × 1019 Hz in free space. Give its two applications. 19. A plane electromagnetic wave travels in vacuum along z-direction. What can you say about the directions of its electric and magnetic field vectors ? If the frequency of the wave is 30 MHz, what is its wavelength? 20. What are the direction of electric and magnetic field vectors, in an electromagnetic wave, related to each other and to the direction of propagation of the wave ? 21. Optical and radio telescopes are built on the ground but X-ray astronomy is possible only from satellites orbiting the earth. Why? 22. The small ozone layer on top of the stratosphere is crucial for human survival. Why? E

160 Physics ALLENÒ Short Answer Type Questions-II (3 Marks each) 23. Which constituent radiation of electromagnetic spectrum is used: 1. in radar 2. to photograph internal parts human body 3. For taking photograph of the sky during light and foggy condition? Give one reason for your answer in each case. 24. Write the order of frequency ranges and one use of each of the following electromagnetic radiation (1) Microwaves (2) Ultraviolet rays (3) gamma rays RACE (SOLUTIONS) Very short Answer type Questions (1 Marks each) 1. Infrared rays 2. 4 × 1011kHz to 7 × 1011kHz www.notesdrive.com 3. RW, MW, UV, X-rays 4. X-rays node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 06_Unit-5.docx 5. Because microwave possesses greater energy and least angular speed. 6. g-rays 7. g-rays 8. 1 : 1 9. 1 : 1 10. Gamma rays, X-rays, Ultraviolet, Infra-red 11. Charge is accelerated or decelerated. 12. Wavelength band: 40 m to 25 m. 13. 109 Hz 14. X-rays 15. Electric and magnetic field vector. It is independent. 16. Zero. 17. Because of their small wavelength, these are not bent by normal obstacles, eg. Air molecules. Short Answer Type Questions-I (2 Marks each) 18. Wavelength l = c = 3´108 m/sec = 6´10-12 m n 5´1019 Hz 19. E and B in x-y plane and are mutually perpendicular and wavelength is 10 m. 20. Electric and magnetic field vector are mutually perpendicular and also perpendicular to the direction of wave propagation, such that electric field E, magnetic field B and propagation vector (vector in the direction of propagation of wave) Kˆ form a right-handed orthogonal system 21. Atmosphere absorbs X-rays, while visible and radio waves can penetrate it. 22. It absorbs ultraviolet radiations from the sun and prevents it from reaching the earth's surface and causing damage to life. Short Answer Type Questions-II (3 Marks each) 23. 1. microwaves because they go straight and not absorbed by atmosphere. 2. X-rays, because these can penetrate light elements like flesh. 3. Infrared radiation because these can penetrate fog and not absorbed by atmosphere. 24. (1) 3 × 1011 – 1010 Hz Use :- Radio and radar communication. (2) 1016 – 7.5 × 1014 Hz Use :- Sterilizing the surgical instruments. (3) 1021 – 1018 Hz Use :-Treatment of cancer E

ALLENÒ CBSE 161 IMPORTANT NOTES node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 06_Unit-5.docx______________________________________________________________________ ______________________________________________________________________ www.notesdrive.com ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ E

162 Physics ALLENÒ IMPORTANT NOTES ______________________________________________________________________www.notesdrive.com ______________________________________________________________________ ______________________________________________________________________ node06\\B0BB-BC\\Kota\\Board Material\\Physics\\CBSE\\CBSE Booklet\\Part-1\\ 06_Unit-5.docx ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ ______________________________________________________________________ E