Science 4

Posttest 6. d B. 6. cylindrical lens 7. d 1. sensitive film 7. simple microscope A. 8. c 2. iris 8. compound microscope 1. b 9. a 3. convex 9. telescope 2. c 10. c 4. power of accommodation 10. laser light 3. d 5. nearsightedness 4. b 5. dReferencesDull, C. E., Metcalfe, H. E. & Williams, J. E. (1960). Modern physics. New York: Holt, Rinehart and Winston, Inc.Hewitt, P. G. (1993). Conceptual physics. (7th ed.) New York: Harper Collins College Publishers.Padua, A. L. & Crisostomo, R. M. (1999). Science and technology IV: Physics. Quezon City: S.D. Publications, Inc.Santos, G. C. & Ocampo, J. P. (2003). Science and technology IV: Physics. Manila: Rex Bookstore, Inc.Sotto, R. L. (2005). Science in today’s world: Physics. Philippine Copyright: SIBS Publishing House, Inc., Makati, Philippines.U.P. Science Education Center. (1984). Physics in your environment: High school science IV. Manila: Textbook Board, Ministry of Education and Culture.Young, H. D. & Friedman, R. A. (1996). University physics. New York: Addison Wesley Publishing Co., Inc. 21

Module 5 Radiation around Us What this module is about Did you know that an effective way oftreating cancer nowadays is with the use ofradiation? Radiation therapy is now beingpracticed by some hospitals in Metro Manila likeSt. Luke’s Medical Center, Makati MedicalCenter and Cardinal Santos Medical Center.The process is very well expressed asradioactivity – the transformation of an atom. In this module you will learn many thingsabout Physics, particularly about radiation. This module includes four (4) lessons such as:  Lesson 1 - Brief Account of Radioactivity  Lesson 2 - Radioactivity  Lesson 3 - Nuclear Reactions: A Menace?  Lesson 4 - Applications of Radioactivity and their Implications Read, enjoy, and discover the secrets of Physics! What you are expected to learn After going through the module, you are expected to: 1. discuss the contributions of Becquerel, Pierre and Marie Curie on radioactivity; 2. discuss and compare the types and properties of ionizing radiation; 3. interpret equations on nuclear reactions; 4. explain Einstein’s matter-energy equivalence; and 5. recognize the significance of the contributions of scientists in nuclear energy and related technology.

How to learn from this module Here’s a simple guide for you in going about the module. 1. Read and follow the instructions very carefully. 2. Take the pretest. It is a simple multiple-choice test provided at the start to determine how much you know about the content of this module. 3. Check your answers against the answer key provided at the last page of the module. 4. Be very honest in taking the test so you know how much knowledge you already have about the topic. 5. Read the different lessons about the earth, sun and moon. 6. Perform all the activities, as these will help you have a better understanding of the topic. 7. Take the self-tests at the end of each lesson for you to determine how much you remember about the lesson. 8. Finally, take the post test at the end of this module. Good Luck and have fun! What to do before (Pretest)Direction: Choose the letter of the best answer. Write your answer on a separatesheet of paper. 1. What is the process by which elements change to other elements by the emission of ionizing particles? a. Radioactivity b. Chemical Change c. Physical Change d. None of these 2. Who is the polish chemist who received 2 Nobel prizes-one in physics and another in chemistry for his/her success in the field of radioactivity? a. Marie Curie b. William Roentgen c. Ernest Rutherford d. Henry Becquerel 2

3. Which of the following is INCORRECT? a. Atoms are made of subatomic particles called electrons, protons and neutrons. b. The electrons are distributed in space like a cloud around the nucleus. c. The nucleus of the atom consists of protons and neutrons. d. The electrons are found inside the nucleus of the atom.4. What do you call the force that holds the nucleus together? a. nucleonic force b. gravitational force c. strong nuclear force d. electromagnetic force5. Helium is 4x as massive as hydrogen. Compared to the size of hydrogen, helium is ___________. a. smaller b. of the same size c. twice as large d. four times as large6. Which among the ionizing radiation can penetrate the farthest into a material? a. a beta particle b. a gamma ray c. an alpha particle d. All have the same penetrating capability.7. The reason alpha rays are easy to stop is that they _____________. a. are relatively big b. slow down easily c. are doubly changed d. All of the above.8. Large nuclei, like uranium, are radioactive because ____________. a. they have too much mass b. there are too many protons c. there are too many isolated neutrons d. they can hold extra particles, like beta rays9. When Uranium (90 protons) ejects an alpha particle, how many protons does the remaining nucleus have? a. 92 protons b. 90 protons c. 88 protons d. 86 protons 3

10. What happens to the atomic number of an element which emits 1 alpha particle and 3 beta particles? a. increases by 1 b. stays the same c. decreases by 2 d. decreases by 111. What happens to the atomic number of an element which emits 1 alpha particle and 2 beta particles? a. increases by 1 b. stays the same c. decreases by 2 d. decreases by 112. A sample of a certain radioactive material has a half-life of 1 year. How much of this radioactive material will be left at the end of 3 years? a. one sixteenth b. one eighth c. one quarter d. one half13. The half-life of most radioactive isotopes is about _________. a. 5700 years b. a few years c. a few seconds d. half lives range from very short to very long14. The half life of a certain isotope is 1 day. At the end of 2 days, how much of the isotope remains? a. one half b. one quarter c. one eighth d. none of it15. Energy released by the sun results from atomic nuclei __________ a. combining b. breaking apart c. None of the above d. Needs more information to say16. Splitting helium would yield ___________. a. a net release of energy b. a net absorption of energy c. neither absorption nor release d. Not enough information to say 4

17. Which shape uses the smallest amount of material when creating a critical mass? a. cube b. cone c. sphere d. elongated box18. If gold were used as nuclear fuel, it would be best ____________. a. fused b. split c. either d. neither19. Suppose hydrogen bombs were exploded in a box that could contain all the energy released by the explosion, the weight of the box after the explosion would be __________. a. less b. more c. the same d. none of the above20. What technique is used by archeologist to determine the age of wooden artifacts? a. Carbon dating b. Radium dating c. Uranium dating d. Polonium dating Key to answers on page 27 5

Lesson 1 A Brief Account of RadioactivityRead this!Do you still remember the word ‘atom’? Atomis the smallest particle of matter. Its era beganduring Becquerel’s time. Becquerel’s discovery ofradioactivity marked the beginning of the modernunderstanding of the atom. Henri Pierre Marie Antoine Henri Becquerel was a physicist and Becquerel Curie Curiean expert in the field of fluorescence. While studyinga fluorescent compound that included an element Fig. 1.1 Scientists who discoveredcalled uranium; he noticed that the material was radiationgiving out a type of a ray that passes through foilwhich he used to wrap the material. He later discovered that this event only happens touranium compound and not with others. Further experiments showed that there were 2distinct types of radiation: the alpha and beta radiation, which consisted of electricallychanged particles. Later, a third type, gamma radiation was discovered which proved to be aform of electromagnetic radiation. Marya Sklodowska (Marie Curie) was born Know this!on November 7, 1867 in Warsaw, Poland. She left forSorbonne in Paris to study chemistry where he met  Nobel Prize – prestigious awardand married another chemist, Pierre Curie (1859- given to a person who has done1906). extraordinary things. In their own research on radiation, they were  Electromagnetic waves – wavesable to discover that a mineral uranium, is 4x as that do not need medium in order to propagate.radioactive as pure uranium. This led them toconclude that the mineral must contain someunknown radioactive element. By 1902, they successfully separated 0.1 gram of theunknown element and called it radium. This breakthrough led them to a Nobel Prize inPhysics in 1903 and a Nobel Prize in Chemistry in 1911. The Curies were the first scientistswho received 2 Nobel Prizes. 6

What you will doActivity 1.1 Try Me!Direction: Answer the crossword puzzle given below. 1 2 1 3 23Across 1. Marie Curie’s husband 2. Becquerel’s first name or given name 3. Process of atom transformationVertical 1. Element discovered by Becquerel to be radioactive 2. Radioactive element discovered by the Curies 3. Home town of Marie Curie. Key to answers on page 27 7

The Nucleus of the AtomBefore we go on, identify the following parts of an atomFig 1.2 The Atom Key to answers on page 27Read this! The atomic nucleus is a very tiny structure of an atom which is composed of particlescalled nucleons. Electrically charged nucleons are the protons and the neutrally chargednucleons are the neutrons. On the average, nucleons have nearly 2000 times the mass ofthe electron. This means that the mass of an atom is practically equal to the mass of itsnucleus alone!Electrons are held close to the nucleus by the protons. The neutrons, on the otherhand, hold the nucleus together. Nucleons are bound by an attractive force known as thestrong nuclear force, which holds the protons and neutronstogether inside the nucleus. 1 H 2 H In an electrically neutral atom, the number of protons 1 1inside the nucleus is equal to the number of electrons in the Hydrogen Deuteriumatomic orbital. A difference in the number of protons and 3 Helectrons makes the atom a charged particle and is known as an 1ion. The number of neutrons in the nucleus, however, has noeffect on the number of electrons an atom may have. This means Tritiumthat any change in the number of neutrons will not affect thechemical properties of an element. Elements having different Fig 1.3 Isotopes ofnumbers of neutrons but have the same number of protons have Hydrogenthe same chemical properties and are called isotopes. 8

The common form of hydrogen has a bare proton as its nucleus. There are howeverdifferent kinds of hydrogen as seen in figure 1.2. They all have the same number of protonsbut different number of neutrons. Thus, they are known as the isotopes of hydrogen:deuterium and tritium. 1 H is a stable element. This means that it has no excess nuclear energy. On the 1other hand, 2 H and 3 H which are isotopes of hydrogen are unstable atoms. They have 1 1excess nuclear energy which is released when the neutrons inside their nuclei decay. What you will do Self-Test 1.1Direction: Answer the following briefly. 1. What is the major contribution of the Curies in the field of radiation that gave them two Nobel prizes? 2. Who initiated the research on radiation? 3. Between what subatomic particles does the strong nuclear force act? 4. How does the number of electrons in an electrically neutral atom compare with the number of protons in its nucleus? 5. What do different isotopes of a given element have in common? How are they different? Key to answers on page 28 9

Lesson 2 RadioactivityRead this! Fig 2.1 The Electromagnetic Spectrum Radiation is energy in transit in the form of high speed particles and electromagneticwaves as seen in Figure 2.1. There are basically 2 types of radiation: the ionizing radiationand the non-ionizing radiation. Take a look at figure 2.1. The electromagnetic waves that we often encounter suchas visible light, radio waves, infrared, microwaves and UV are electromagnetic waves thatdo not carry enough energy to separate molecules or remove electrons from an atom. Suchwaves are called non-ionizing radiation. The electromagnetic waves, on the other hand, such as x-rays, gamma rays andcosmic rays are known as ionizing radiation. These are the rays that carry amounts ofenergy large enough to remove electrons from the atom, thus making the atom a charged oran ionized particle. In the same manner, some atoms are unstable and are calledradioactive. These atoms eventually disintegrate into a totally new atom. This process ofspontaneous transformation of an unstable atom whichresults in the emission of radiation is called radioactivity. Take a look at Figure 2.2. A single or lone neutron is Stable neutronan unstable neutron. While a neutron with a proton is astable one. Neutrons without nearby protons decay into a +proton and an electron (Figure 2.2). All nuclei that decay inthis manner are known to be radioactive. Radioactive atoms Unstable neutrondecay and emit three distinct types of rays. These are thealpha particle (α) for an alpha decay, a beta particle (β) for a +beta decay, and gamma ray (γ) for a gamma decay. Fig 2.2 Stable and Unstable Neutron 10

Alpha particles consist of two protons and two neutrons in 4 He Alpha particlethe form of atomic nuclei. They carry a positive electrical 2 Beta particlecharge and are emitted from naturally occurring heavyelements such as uranium. Since alpha particles are relatively 0 elarge they collide readily with matter and quickly loses this 1energy, thus they have little penetrating power. Sheets ofpaper and skin can easily block or stop alpha particles. Beta particles, on the other hand, are fast moving Gamma rayelectrons ejected from the nuclei. They are smaller than thealpha particle, thus they have greater penetrating capability.They can penetrate up to 2 cm of water or human flesh andcan only be stopped by a sheet of aluminum. Fig 2.3 Ionizing particles andX-rays and gamma rays are transmitted through radiationwaves. X-rays are generally artificially produced whilegamma rays are generally emitted from the atomic nucleus. Both have high penetratingpower and can easily pass through the human body. Only thick barriers of concrete, lead orwater can be used to stop them. Neutrons are particles, that are highly penetrating. They usually originate from thesplitting (nuclear fission) of atoms in a nuclear reaction. Water and concrete are the mostcommon shields against neutron radiation. What you will do Activity 2.1 Ionizing RadiationDirection: Identify the ionizing radiation that can penetrate the given materials. Key to answers on page 28 11

Did you know that Uranium- 92 90 + 2238 can decay and become 146 144Thorium- 234? When a nucleus of 2an atom emits an alpha or a betaparticle, a different element is U238 23940Th + 4 Heformed. This changing of one 2element to another is called 92 transmutation. (Daughter nucleus) (alpha particle) (Parent nucleus) Fig 2.4 Transmutation of a radioactive element Take a look at figure 2.4. Uranium-238 has 92 protons and 146 neutrons. The sum ofthe protons and neutrons is 238. This is known as the atom’s mass number. The massnumber of an atom is the totalnumber of particles inside theatomic nucleus. If an alpha particle( 4 He ) is emitted then the mass 90 91 + 2 144 143number of Uranium is decreasedby 4 while the number of protons isdecreased by 2. This results to a 23940Th  234 Pa + 0 enucleus with a mass number of 234 91 −1(238-4=234) 90 and protons (92- (Parent nucleus)2=90). If we consult the periodic (Daughter nucleus) (beta particle)table of elements, the element with90 protons and a mass number of Fig 2.5 Beta Decay of Thorium-234234 is Thorium. This means thatUranium (parent nucleus) has become thorium (daughter nucleus) when an alpha particle isemitted. This radioactive decay is particularly called alpha decay. When this happens,energy is then released in three forms: gamma radiation, kinetic energy of the alpha particleand kinetic energy of the thorium. Take a look at figure 2.5. Thorium is still radioactive and can possibly emit a betaparticle. Remember that a beta particle is an electron ejected from the nucleus. When a betaparticle is ejected, a neutron changes into a proton. For thorium, beta emission leaves itsinitially 90 protons with fewer neutrons and an additional proton. Thus, the new nucleus has91 protons and 143 neutrons. In the periodic table of elements the element which has 91protons and 143 neutrons is Protactinium. 12

Gamma emission has no effect on the mass Th Th234 234number or on the number of protons. Thus, for 90  90 + γThorium, gamma decay results to Thorium of Fig 2.6 Gamma decay of Thorium-234lesser energy.Remember this! The number of nucleons on the left side of the equation (reactants) must alwaysequal the number of nucleons on the right side of the equation (products). What you will do Activity 2.2 Ionizing RadiationDirection: Identify the nucleus of the new element designated by X in each of thefollowing reactions.1. 226 Ra X + 4 He 88 22. 234 Pa X + 0 e 91 13. 59 Fe X + γ 264. U234 X + α 92 Key to answers on page 28 13

The Half-lifeDo you have any idea when will half of Radium-226decay? The time needed for half of the active atoms to 226 Radecay is known as half life. This means that half-life is theradioactive decay rate. In the case of Radium-226, its half-life is 1620 years. This means that after 1620 years, half ofthe 5-g sample which is 2.5 grams will decay leaving a 2.5 gactive radium-226. Then after another 1620 years, half of theremaining 2.5 grams which is 1.25 grams will decay leaving 1.25 g active radium – 226.Rates of radioactivity are remarkably constantand are not affected by any external conditions suchas changes in pressure and temperature. Uranium-238 for example has a half-life of 4.5 billion years.This is measured using radiation detectors such as aGeiger counter and scintillation counter. A Geigercounter detects incoming radiation by its ionizing Geiger Counter Scintillation Countereffect on enclosed gas in a tube. A scintillationcounter, on the other hand, detects incomingradiation by flashes of light that are produced when Fig 2.7 Radiation detectorscharged particles or gamma rays pass through it. Thehalf-life of an isotope is related to its rate ofdisintegration. Generally, half-life is shorter for more active substances. The half-life can becomputed from the rate of disintegration, which can be done in the laboratory. What you will do Activity 2.3 Half-LifeObjective: To develop an understanding of half life of radioactive atoms.Materials: 100 25-centavo coins, graphing paperProcedure: 1. Place the 100 25-centavo coins in a shoe box. 2. Pour out the coins on a clean table. 3. Take out the coins that show the head. The coins that showed the head represents the decayed radioactive material. 4. Count how many coins are left after the 1st throw. Record your data on the table provided. 14

5. Place the remaining coins in the box. Then again pour out the coins on the clean table. 6. Take out the coins that show the head. 7. Count how many coins are left. Record your data on the table provided. 8. Continue doing the activity until only 2 or 3 coins are left.Data and Results Number of throws Number of decayed Number of coins coins left 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Analysis:1. Using your data what do you notice about the rate at which the coins “decay” as their number decreases?2. Plot the graph of the number of coins left (N) against the number of throws (t). The number of coins should be along the vertical axis while the number of throws should be on the x-axis. 15

N 0 t3. How would you describe the graph? Key to answers on page 294. Describe in your own words what half-life is. What you will do Self-Test 2.1Direction: Answer the following briefly.1. Identify the daughter nucleus in the decay of U234 by alpha particle emission. 922. Name the element that results from the alpha decay of polonium.3. If a sample of a radioactive isotope has a half-life of 2 years, how much of the original sample will be left at the end of the 4th year? Key to answers on page 29 16

Lesson 3 Nuclear Reaction: A menace? Take a look at figure 3.1. These are 2 Fig 3.1. Nuclear Reactionsinstances of nuclear reactions, one brings Greater nuclear force than electrostatic forceabout destruction while the other is aconstant source of energy of the planet. Critical deformation Greater electrical force than nuclear force The atomic bomb that hit Hiroshima Fig 3.2. Forces within the atomic nucleusduring World War II was discovered in 1939.It involved the splitting of the atoms, a Fig 3.3. Chain reactionprocess known as nuclear fission.Take Note of these!Nuclear Fission The nucleus of the atom is heldtogether by a strong nuclear force. When thestrong nuclear force is greater than therepulsive electrical force within the nucleus,then the nucleus maintains its shape asshown in figure 3.2. However, if the repulsiveelectrical force increases and the nuclearforce decreases to a critical level, the nucleuselongates. The nucleus further elongates withincreasing electrical force until it splits. Oneway for an atom to split is when it absorbs aneutron. Take a look at figure 3.3. This iswhat happens when one neutron starts thefission of a uranium atom. It could result toa combination of smaller nuclei emitting twoneutrons. These two new neutrons in turncan cause the fissioning of two other atomswhich in turn can cause more atomicfissioning. This makes a chain reaction.Specifically, fission reaction occurs to therare isotope of U-235. If a chain reactionoccurs in a pure U-235, a great explosionwill likely to occur. This makes U-235 adangerous isotope of Uranium-238. Butdon’t worry, it is very difficult to separateenough U-235 from U-238 for an atomicbomb. In fact, it took the scientists more17

than two years to extract enough U-235 from uranium ore to make one atomic bomb that hitHiroshima in 1945.Think about it!Nuclear Fusion Take a look at the picture of the sun. What color do you see? Is this the real color ofthe sun? What about the energy or light it emits? Is it also colored yellow? The sun is reallya yellow star. This is because the sun is a middle-aged star. The color of the star tells us itstemperature. Yellow stars have surface temperatures of about 6000 oC. But the inside of thesun is much hotter than the surface.Astronomers believe that the inside temperature of the sun is over 13 million degreesCelsius (13 000 000 oC). This very high temperature on the inside makes it possible for thesun to undergo a process called nuclear reaction. In a nuclear reaction, the atomic nucleiare changed. Atomic nuclei combine in the sun’sinterior. This kind of nuclear reaction is calledthermonuclear fusion. Since the sun is about80% hydrogen, 18% helium, and 2% otherelements deep inside the sun, the hydrogennuclei fuse or combine to form a nucleus ofhelium. HeIn this reaction, four hydrogen nucleicombine to form one helium nucleus. The massof the helium nucleus is usually much less thanthe combined mass of the four hydrogen nuclei.This missing mass is a matter that is changed 4 H  He + Energyinto an amount of energy. This conversion ofmass to energy is done using Einstein’s principleof matter-energy equivalence. It is usually Fig 3.4. Thermonuclear Fusionexpressed in his famous equation: E = mc2where E = the equivalent energy of a difference in mass m = difference in mass after a nuclear reaction c = conversion factor which is also known as the speed of light = 3 x 108 m/s This equation means that any change in the mass of a radioactive substance after anuclear reaction (nuclear fission or nuclear fusion) is converted into a form of energy. In thecase of the sun, thermonuclear fusion results to a difference in mass which is detected inthe form of electromagnetic waves such as light, UV and microwaves. 18

What you will do Activity 3.1 Reminiscing Nuclear Energy Look for articles or pictures of the Bataan Nuclear Power Plant. Identify what nuclearreaction is used to acquire energy. What are the possible advantages and disadvantages ofits construction and operation in the Philippines (Cite at least 2 advantages and 2disadvantages). Key to answers on page 29 What you will do Self-Test 3.1Direction: Answer the following very logically. 1. What happens when U-238 absorbs a neutron? 2. What becomes of the loss in mass of nucleons when heavy atoms split? 3. What becomes of the loss in mass of nucleons when light atoms fuse to become heavier ones? 4. Why are fusion reactors not yet a present day reality like fission reactors? Key to answers on page 29 19

Lesson 4 Applications and Implications Fig 4.1. Background radiation Fig 4.2 Chest X-ray Did you know that most radiation thatwe encounter originate in nature? It is in theground where you stand on, in the bricks andin the building. Even air is slightly radioactive.This natural background radiation is believedto be present before we even know about it. Itis believed to be existing before the humanrace existed.How much radiation do you receive when youundergo chest x-ray? Is this amount ofradiation harmful to the tissue?Read this! The amount of ionizing radiation or ‘dose’received by a person is measured in terms of theenergy absorbed in the body tissue and isexpressed in gray. One gray (Gy) is one jouledeposited per kilogram of mass. Equal exposureto different types of radiation expressed as graydoes not necessarily mean the same biologicaleffects. For example, one gray of alpha radiationwill have greater effect than one gray of betaradiation. The unit known as sievert (Sv) is usedto express the radiation effect as effective dose.Accordingly, 2-10 sievert doses are believed tocause severe radiation sickness and can be fatal.20

Table 4.1. Effective dose in Sv and their corresponding biological effects.Effective dose Biological Effect1 Sv Threshold for causing immediate radiation sickness100 mSv and The probability of cancer increases with doseabove20 mSv/yr Estimated effective dose of people who work in mines and hospitals Typical background radiation from natural sources. This is2 mSv/year close to the minimum dose received by all humans anywhere on Earth.What you will doActivity 4.1 Computing my effective dose We live in a radioactive world. By filling out this form, you will get an idea of theamount of radiation you are exposed to every year. The average Filipino is exposed tobetween 100 and 300 units each year. YOUR ANNUAL TOTALCosmic radiation that reaches earth: 44Because cosmic radiation is modified by the atmosphere ______ add 1 for every 100 feet above sea level ______If your house is brick or concrete add 45 stone add 50 wood add 35Ground radiation 15Water, food, air radiation 25Nuclear weapons testing fallout 4If you have had a chest x-ray this year add 9 for each one: ______If you’ve had intestinal x-ray add 210 ______For each 1500 miles you’ve flown in an airplane during the ______ year add 1: 21

If you live within 5 miles from a nuclear plant add 0: ______If you sleep with your spouse add 0.1: ______ TOTAL ______________*Note: The unit in this computation is mSv. Check out table 4.1 if your annual dose is withinthe optimum range. Key to answers on page 29 Although radiation is a menace at high levels, Radiationradiation in correct doses has many uses. Medical and Therapydental x-rays discern hidden problems. Radiation is used todiagnose ailments. Cancer patients are treated with Sterilizationradiation. Fig 4.3. Applications of Aside from its medical applications, radiation can also Radiationbe used as a technique by archeologist to establish thedates of wooden artifacts and skeleton. This process isknown as carbon dating. The dating of older, but non-livingthings like the planet earth is done using uranium datingtechnique. Further, nuclear reactions can produce largeamounts of energy that could sustain life on earth for a longtime. We all benefit from a multitude of products andservices made possible by the careful and responsible useof radiation22

What you will do Self-Test 4.1Direction: Answer the following very briefly. 1. Cite at least 3 applications of radiation. 2. What is the probable reason why some people think of radiation as a menace? 3. Differentiate carbon-dating and uranium-dating. Key to answers on page 30 Let’s summarize 1. Radioactivity is the process of atomic transformation. 2. Radiation is an energy released in the form of high speed particles or electromagnetic waves during a nuclear reaction. 3. Henry Becquerel discovered that uranium is radioactive. Marie and Pierre Curie discovered the element radium. 4. The isotope of an element has the same number of protons as the element but has different number of neutrons. 5. Ionizing radiation has enough energy to separate molecules or remove electrons from an atom while non-ionizing radiation does not have enough energy to remove electrons from an atom. 6. Radioactive atoms decay and emit three distinct types of rays: alpha particle in an alpha decay, beta particle in a beta decay, and gamma ray in a gamma decay. 7. Transmutation is the changing of one element to another by emission of an alpha particle or a beta particle. 8. Half-life is the time needed for half of the active atoms to decay. 9. Geiger counter is a radiation detector that detects incoming radiation by its ionizing effect on enclosed gas in a tube. Scintillation counter is a radiation detector that detects incoming radiation by flashes of light that are produced when charged particles or gamma rays pass through it. 10. There are two types of nuclear reactions: nuclear fusion and nuclear fission. Nuclear fission is the splitting of atom that releases tremendous amount of energy while nuclear fusion involves combining the nuclei of atom to produce large amounts of energy. 11. Radiation can be a menace through the production of atomic bombs. However, radiation is of great help to humans especially in the field of medicine and archeology, and as an energy source. 23

PosttestDirection: Choose the letter of the best answer. Write your answer on a separate sheet of paper1. The energy released in the form of high speed particles or electromagnetic waves during a nuclear reaction is known as ____________. a. chemical energy b. electrical energy c. stored energy d. radiation2. The physicist and the specialist in the field of fluorescence who discovered that the element uranium is radioactive is ______________. a. Marie Currie b. William Roentgen c. Ernest Rutherford d. Henri Becquerel3. Which of the following compose the nucleons? a. electrons, protons and neutrons. b. electrons and protons c. neutrons and electrons d. protons and neutrons4. What do you call the force that maintains the electrons in their orbitals? a. nucleonic force b. gravitational force c. electrostatic force d. strong nuclear force5. Helium is 4x as massive as hydrogen. Compared to the size of hydrogen, helium is ___________. a. smaller b. of the same size c. twice as large d. four times as large6. Which among the ionizing radiation can penetrate the least into a material? a. an x-ray b. a beta particle c. a gamma ray d. an alpha particle 24

7. The reasons alpha rays are easy to stop is that they _____________. a. are relatively big b. slow down easily c. are doubly changed d. All of the above.8. Large nuclei, like radium are radioactive because ____________. a. they have too much mass b. there are too many protons c. there are too many isolated neutrons d. they can hold extra particles, like beta rays9. When Uranium (90 protons) ejects a beta particle, how many protons does the remaining nucleus have? a. 92 protons b. 91 protons c. 90 protons d. 89 protons10. What happens to the atomic number of an element which emits 1 alpha particle and 1 beta particle? a. increases by 1 b. stays the same c. decreases by 2 d. decreases by 111. What happens to the atomic number of an element which emits 1 alpha particle? a. increases by 1 b. stays the same c. decreases by 2 d. decreases by 112. A sample of a certain radioactive material has a half-life of 1.5 year. How much of this radioactive material will be left at the end of 3 years? a. one sixteenth b. one eighth c. one quarter d. one half13. The half-life of most radioactive isotopes is about _________. a. 5700 years b. a few years c. a few seconds d. half lives range from very short to very long 25

14. The half life of a certain isotope is 2 days. At the end of 2 days, how much of the isotope remains? a. one half b. one quarter c. one eighth d. none of it15. Which of the following nuclear reactions is responsible for the release of energy by the sun? a. Nuclear Fission b. Thermonuclear Fusion c. None of the above d. Needs more information to say16. When an element splits, the process would yield ___________. a. a net release of energy b. a net absorption of energy c. neither absorption nor release d. Not enough information to say17. Which shape uses the smallest amount of material when creating a critical mass? a. cube b. cone c. sphere d. elongated box18. If gold were used as nuclear fuel, it would be best ____________. a. fused b. split c. either fused or split d. neither fused nor split19. An experimenter finds that 50% of a sample of U-238 has decayed. Since U-238 has a half-life of 4.5 billion years, the sample’s age is about __________. a. 0.60 billion years b. 1.12 billion years c. 2.25 billion years d. 4.50 billion years20. The reason carbon-dating works is that ______________. a. plants and animals are such strong emitters of carbon-14 b. after a plant or animal dies, it stops taking in fresh carbon-14 c. there is so much non-radioactive carbon dioxide in the air d. when a plant of an animal dies, it stops producing oxygen Key to answers on page 30 26

Key to AnswersPretest 11. B 1. A 12. B 2. A 13. D 3. D 14. B 4. C 15. A 5. D 16. A 6. B 17. D 7. D 18. B 8. C 19. C 9. C 20. A 10. ALesson 1Activity 1.1 2R 1U A 1P I E R R E 3R A D I I A U 3P 2H E N R I M OACT I VI T Y LU AM N D Orbital Electron NucleusFig 1.2. The Atom 27

Self-Test 1.1 1. The discovery of Radium. 2. Antoinne Henri Becquerel 3. Protons and neutrons 4. The number of electrons is equal to the number of protons in an electrically neutral atom. 5. Isotopes of a given element have the same number of protons or atomic number but have different number of neutrons.Lesson 2 Activity 2.1Activity 2.2.1. 222 Rn 862. U234 923. 59 Fe 264. 23900Th 28

Activity 2.3. Analysis 1. As the number of coins decreases, the rate at which the coins “decay” also decreases. This is because as the atoms are disintegrating all the time, there will be fewer and fewer atoms left which still have to disintegrate. 2. N t 3. The graph shows a decreasing N as t increases. 4. Half life is the time it takes for the amount of radioactive substance to be reduced to half its original value.Self-Test 2.1. 1. U234  23900Th + 4 He 2 92 (daughter) 2. 209 Po  204 Pb + 4 He 84 82 2 Lead (Pb) is the element that results from alpha decay of polonium 3. One-fourthLesson 3Activity 3.1 1. Nuclear Fission is used as a process of acquiring energy in Bataan Nuclear Power plant. 2. Advantages: a. New source of energy b. Additional employment or jobs Disadvantages: c. Radiation pollution d. Cycle disruption 29

Self-Test 3.1 1. U-238 will emit a beta particle and becomes neptunium. 2. Loss in mass is radiated as energy. 3. Loss in mass is radiated as energy. 4. Sustained fusion reaction is not yet possible on earth.Lesson 4 Activity 4.1 – Answers may vary Self-Test 4.1 1. Applications a. Cancer treatment b. Carbon-dating c. Source of energy 2. Disadvantages a. Construction of destructive atomic bombs b. Excessive radiation use brings about cancer c. Radiation pollution 3. Carbon-dating is a technique used in dating dead living organisms while uranium-dating is a technique used in dating older nonliving things.Post Test 11. C 12. C 1. D 13. D 2. D 14. A 3. D 15. B 4. C 16. A 5. D 17. C 6. D 18. C 7. D 19. D 8. D 20. B 9. B 10. D -End of Module- 30

ReferencesHalliday, D., Resnick, R. & Krane, K. (1994). Fundamentals of physics. Singapore: John Wiley & Sons Inc.Hewitt, P. (1989). Conceptual physics (6th Ed.) London: Scoot, Foresman and CompanyHeuvelen, A. (1986). Physics. A general introduction (2nd Edition). Sta. Cruz, Manila: UNI-ED Inc.,Jones, E. & Childers, R. (1999). Contemporary college physics. NY: Mc Craw-Hill Co.Morales, M., Corpus, A., Corpus, E., Dayao, A., Sotto, R. (2000). WorkText in physical sciences. Manila: PNU PressYoung, Hugh. D. (1996). University physics (9th Edition). NY : Addison-Wesley Publishing Co.Physics Classroom Tom Henderson © 1996-2004. Retrieved on January 5, 2005 form www.physicsclassroom.com 31

Module 8 Magnetism What this module is about Everybody is familiar with a toy magnet, that mysterious little U-shaped device thatpicks up needles or pins and holds them indefinitely in what seems to be like magic. As achild you probably played with small magnets. But magnet is far from being a mere toy. It isan essential part of machines, tools and some measuring devices. You have heard of amagnetic compass that helps navigators keep their course at sea. When you hold a phonereceiver to your ear, a magnet records the vibrations set up by the voice of the persontalking at the other end. Electric motors also contain magnets to function. Particleaccelerators like cyclotron contain thousand of magnets as well. Electricity and magnetism cannot be separated. Magnetism plays an important role inthe study of electricity. Whenever electric current appears, there is magnetism. Theoperation of many electrical devices such as radios, TV sets, motors and other devicesdepends on the magnetic effects of electric current. This module presents the discovery of magnetism and some of the fundamentalexperiments and laws showing the relationship between electricity and magnetism. Inreading this module, you should pay attention to the nature of the force exerted on movingcharges by a magnetic field. In addition, you need to understand the way in which anelectric current produces a magnetic field. You will also learn how two important current-carrying shapes of wire: a long straight wire and a circular loop or solenoid producemagnetic field. This module discusses the following topics:  Lesson 1 - Discovery of Magnetism  Lesson 2 - Magnets and Magnetic Field  Lesson 3 - Electromagnetism Read this module and see the wonders of electricity and magnetism and theircontributions to the world of technology. So, start and enjoy. 1

What you are expected to learnAfter going through this module, you are expected to: 1. discuss the history of magnetism; 2. describe the different kinds of magnets and their properties; 3. list some uses of permanent magnets; 4. explain what is meant by magnetic field and how it is detected; 5. describe magnetic field; 6. show how magnetic fields and electric currents are related; 7. describe the way an electromagnet is made and the kind of magnetic field it produces; 8. state the effect that a magnetic field has on electric current; 9. recognize the conditions under which a magnetic field can be used to produce electric current; 10. explain how the interaction of magnetic fields produces movement in a motor; 11. illustrate the components of a typical household electrical circuit; 12. describe the functions of fuses and circuit breakers and tell how they work; 13. describe a generator and the way it produces electric energy; and 14. describe a transformer and explain how it works. How to learn from this moduleHere’s a simple guide for you in going about the module:1. Read and follow instructions carefully.2. Answer the pretest in order to determine how much you know about the lessons in this module.3. Check your answers with the given answer key at the end of this module.4. Read each lesson and do activities that are provided for you.5. Perform all the activities diligently to help and guide you in understanding the topic.6. Take the self-tests after each lesson to determine how much you understood the topic.7. Answer the posttest to measure how much you have gained from the lessons. 2

What to do before (Pretest)I. Choose the letter(s) of the BEST ANSWER. Write your answers on a separate sheet of paper1. The N pole of a compass needle points to the north magnetic pole of the earthbecause that pole isa. an S pole c. a large iron depositb. an N pole d. near the north geographic pole2. If the poles of two magnets repel each other a. both poles must be S poles. b. both poles must be N poles. c. one pole is an S and the other is an N. d. both poles are of the same kind.3. Magnetizing a piece of iron is a process by which a. magnetic atoms are added to the iron. b. magnetic lines of force are brought into line. c. existing atomic magnets are brought into line. d. each atom in the iron is converted into a magnet.4. A magnetic field can make a compass needle turn because the field a. attracts N poles. b. is produced by a magnet. c. comes from the center of the earth. d. exerts forces on the atomic currents in the compass needle.5. A primary solenoid connected to a battery is inside a secondary solenoid. It is not possible to induce a current into the secondary coil by a. turning the primary current off. b. moving a core into the primary coil. c. pulling the primary out of the secondary coil d. running a steady current through the primary coil.6. A magnet will attract a wire if a. the wire is long. b. the wire has a small mass. c. the wire exerts an electric force. d. the wire has current flowing through it. 3

7. The iron atom acts as a magnet because a. it has an equal number of protons and electrons. b. the electrons have a spinning motion. c. the electrons have negative charge. d. the neutrons have no charge.8. A steel sewing needle can be made into a magnet by a. banging it on a table. b. soaking it in mercury. c. placing it near a compass. d. stroking it with a magnet in one direction only.9. A piece of copper cannot be made into a magnet because a. copper cannot be charged. b. the domains are already aligned. c. the copper atoms have no charge. d. electrons spinning in opposite directions in copper cancel each other.10. To increase the strength of an electromagnet, a. increase the current in the coil. b. add an iron center in the coil. c. increase the number of loops in the wire. d. all of the above11. If a magnet is brought near a magnet suspended on a string, the a. N poles attract each other. b. N poles attract the S poles. c. S poles attract each other. d. N poles repel the S poles.12. A device that turns electric energy into sound energy isa. a speaker . b. a generator.c. a VCD player. d. a transformer.13. Substances that are slightly attracted by strong magnets are said to bea. diamagnetic. b. ferromagnetic.c. paramagnetic. d. none of these.14. The lines of force of unlike poles placed near each other a. curve away from each other. b. connect the poles. c. cancel each other. d. none of these. 4

15. The scientist who discovered that an electric current can affect the action of a magnetic needle was a. Ampere. b. Oersted. c. Faraday. d. Gilbert.II. Complete each statement by supplying the correct term or phrase. 1. The N pole of a magnet will be attracted to the _____ pole of another magnet. 2. Alloys and ceramics are used to make _______magnets. 3. The S pole of the earth’s magnetic field is located in ________. 4. Many magnetic lines of force go into a magnet at its ________. 5. A suspended solenoid will rotate until it is lined up with the earth’s ______. 6. Regions containing groups of atoms that act like small magnets are called _________. 7. The relationship and interaction between electricity and magnetism is called ___________. 8. Like poles of magnets ________each other. 9. ______ are objects that attract material containing iron and they always face the same direction when moving freely. 10. Natural magnets are made of iron ore called ________. Key to answers on page 32Lesson 1 Discovery of Magnetism Have you ever used a compass to find a direction? If you have, you are doingsomething that was first done by the Chinese in the twelfth century. Historians believe thatthe Chinese were the first to build compasses to help them navigate. They made use of aproperty of certain materials that had been discovered centuries before – magnetism. To know more about the discovery of magnetism, do this activity. 5

What you will do Activity 1.1 Read the history of magnetism and answer the questions after the selection: MAGNETS: KNOWN SINCE ANTIQUITY Magnetism, the natural force that causes magnets to function as they do, becameknown to people many centuries ago. They knew that the black metallic ore are calledloadstone. It has the property of drawing particles of iron to it. Pins, needles and nails are The Greek philosopher named Thales, who attracted to the lodestone lived during the sixth century B.C., is said to have been the first to observe this property. After hishis atomic theory. time, the lodestone was often mentioned in ancient writings. It was given the name “magnet” after Magnesia, a district in the Asia Minor where large magnetic deposits are found. Years later, they found out that the thing they called magnet does not only attract iron rings but also attract other rings suspended from one another forming a long chain. The Roman Lucretius, who lived in the first century B.B., tried to explain magnetism in terms of There are many legendary accounts of the properties of magnet. The Arabian Nightscontains the story of ship that approached an island made of magnetic rock. The ship fellcompletely to pieces because all the iron nails were pulled out of it through the attraction ofthe rock. Another tale was based on the story of a shepherd named Magnes. One day whenhe was tending his flock of sheep on the slopes of Mount Ida in Asia Minor, he noticed thatthe iron tip of his staff was being pulled toward the ground. He dug up the ground and foundout that the large deposit of lodestone was attracting his staff. Thereafter the lodestone wascalled magnet in honor of the shepherd who had discovered it, and later was calledmagnetite. Scholars have pointed out that this story originated long after the word “magnet”was commonly used. 6

What you will do Self-Test 1.1 Test your understanding by completing the blanks.1. The black metallic ore that has the property of attracting pieces of iron are called _____________.2. The natural force of attracting pieces of iron is called ___________.3. The word magnet was believed to have been derived from the name of a shepherd named ______________.4. Lodestone was later called ____________ for its magnetic property.5. _________ was a Greek philosopher who first discovered the magnetic property of lodestone. Key to answers on page 32Lesson 2 Magnets and Magnetic Fields In the course of the centuries, much of the mystery that once surrounded magnetismhas been dispelled. Today, the lodestone or the natural magnet is no longer familiar in thestudy of magnetism because practically all magnets nowadays are artificial. This lessondicusses the different types of magnets, their properties and magnetic fields.A. Magnetic Substances A substance that possesses magnetic properties is a magnet. It attracts iron and faces the same direction when moving freely. All materials have the property of being attracted or repelled. Substances like iron and steel are strongly attracted to magnets. These substances are called ferromagnetic. Nickel and cobalt are also ferromagnetic. These materials are often called magnetic materials. Some substances, such as wood, aluminum, platinum and oxygen, are just slightly attracted by strongmagnets. These substances are called paramagnetic. Substances that are slightly repelledby magnets are diamagnetic. Table salt, mercury, zinc and gold are diamagneticsubstances. 7

Substances that are already magnetizedare called magnetite. These are callednatural or permanent magnets. Lodestonesare permanent magnets. Materials that canbe made into magnets are called artificial magnets.Artificial magnets are made by induced magnetism.This is done by stroking ferromagnetic materialsin the same direction several times with a magnet.This process is called magnetization. ALNICOmagnet is permanent magnet containing aluminum,nickel and cobalt. Temporary magnets are thoseof soft iron that are easy to magnetize and losestheir magnetic property very easily. Electromagnet is an example of temporary magnet. It isa magnet that can be switched on and off. It is used to lift heavy objects in industrial sitesand forwarding businesses. Permanet magnets are used in radio speakers, audio-videodevices and other electrical appliances. What you will do Activity 2.1 Making an artificial magnet by induced magnetismProblem: How to make an artificial magnetMaterials: screw driver, magnet (circular magnet from defective radio speaker) pins, clips and nailsProcedure: 1. Gather all the materials needed. 2. Stroke the end of a screwdriver with the magnet. (Do it in one direction only) 3. Place the screwdriver near pieces of paper clips, pins or nails. Observe what happens. ___________________________________________ ________________________________________________________ Key to answers on page 32 8

B. Magnets and Magnetic ForcesLook at the pictures above. The areas of greatest magnetic force are called magnetic poles.Every magnet has two poles. You cannot produce a magnet with only one pole. The end of the magnet that points north is called the north magnetic pole, (N pole),and the end that points south is the south magnetic pole, (S pole). What you will do Activity 2.2 The diagram below illustrates a bar magnet that is suspended by a string. Anotherbar magnet is brought near it. Study the arrows in the diagram and answer the questionsbelow. The N pole of a The S pole of a The S pole of a The N pole of amagnet is brought magnet is brought magnet is brought magnet is broughtnear the S pole of near the S pole of near the N pole of near the N pole of the suspended the suspended the suspended the suspended magnet magnet magnet magnet 9

Answer the following questions: 1. What happens to the suspended magnet when the S pole of the other magnet is brought near its N pole? ____________________________________________________________________ 2. What happens to the suspended magnet when the N pole of the other magnet is brought near its N pole? ____________________________________________________________________ 3. What happens to the suspended magnet when the N pole of the other magnet is brought near its S pole? ____________________________________________________________________ 4. What happens to the suspended magnet when the S pole of the other magnet is brought near its S pole? ____________________________________________________________________ Key to answers on page 32Rules of Magnets You’re right in your observations regarding the magnets. The diagrams belowillustrate the rules of magnets. Refer to the diagrams below:Like poles repel. Opposite poles attract. 10

Uses of Magnets There are also five elements that can be made into magnets: iron, cobalt, nickel,aluminum, gadolimium and dysprosium. None of these elements can be magnetizedpermanently. To make a permanent magnet, you need an alloy. An alloy is a mixture of twoor more metals. The classic material for making a permanent magnet is steel, an alloy ofcarbon and iron. The best material for permanent magnet is magnequench, which wasinvented in 1985. This material is mostly iron, with a little neodynmium and boron added. Ships use compasses to find the correct course through vast areas of oceans whereno land is in sight. A ship’s compass is a permanent magnet attached to a card marked indegrees that floats in alcohol. Magnets are made in many sizes and shapes. There are several magnets hidden inyour home. Electric clocks, motors, stereos, loudspeakers and television sets all containmagnets. One magnet that is easy to find is the magnet found on the door of yourrefrigerator.C. Magnetic Domains, Magnetic Fields and Magnetic Lines of Force Most materials cannot be magnetized. Iron and a few other materials such as steel,nickel and cobalt can be magnetized. These materials have regions called magneticdomains. Magnetic domains, which are clusters of many atoms, can be thought of as tinymagnets. Substances that can be magnetized can be thought of as consisting of many tiny magnets. How does the arrangement of the “tiny magnets” differ between the unmagnetized and magnetized substances?Look at this! BEFORE: When the material is unmagnetized, the domains are not lined up in a definite way. They are randomly arranged. AFTER: When the material is magnetized, the domains line up in a definite pattern. All the north poles point in one direction, and the south poles in the other. 11

So, if you cut a magnet in half, the cut endsbecome poles. You then have two similarmagnets, each with an N pole and an S pole.Breaking a magnet does not greatly affectthe alignment of domains in the pieces, soeach piece is still a magnet. The closer you bring two magnets together, the stronger the force between thembecomes. Move them apart and the force gets weaker. If you move them apart farther, youwill eventually feel no force. The force changes strength as you move within the magnet’smagnetic field. A magnetic field is the space around a magnet in which its force affectsobjects. A good picture of a magnetic field can be made by sprinkling iron filings around amagnet. (See figure below.) What you will do Activity 2.3 Drawing Magnetic Lines of ForceMaterials: bar magnet (2) iron filings plain sheet of paperProcedure: 1. Place two bar magnets flat on the table with the N poles about 2 cm apart. 2. Cover the magnets with a thin sheet of plain paper. 3. Sprinkle the iron filings on the paper gently until the filings line up. 4. Make a sketch showing how the magnetic lines of force are arranged. 5. Where is the magnetic field strongest? 12

If the materials are not available at home, refer to the following figures:Figure A: Figure B: 1. Trace the path of the iron filings in each figure. 2. What do you observe?______________________________________Discussion: The magnetic field changes the filings into little magnets that attract one another. Thismakes the filings form long and thin chains. The chains line up in the shape of the magneticfield.Analysis: Figure A shows the magnetic field around a bar magnet. The arrowheads show the direction of the magnetic lines of force, which come out of the N pole and enter the S pole. The concentration of lines of force at the poles shows that the field is strongest there. Fig. A: Bar Magnet Figure B shows the magnetic field around a U-shaped magnet. The shape crowds the lines of force together in between the two poles. This means that the magnetic force between the poles becomes very strong. This is also the reason why a horseshoe magnet can lift greater weights than a bar magnet. Fig. B: U-shaped magnet 13

(a) (b) In studying magnets in 1820s, Michael Faraday described magnetic fieldsFig. C: Magnetic Lines of Force through magnetic lines of force (Fig. (a) between two unlike poles C) (b) between like poles Magnetic lines of force never overlap even when the poles of the two magnets are brought close to one another.What you will do Self-Test 2.1Arrange the jumbled letters to form the word(s), that best fits the statement.1. Natural magnets COILAN2. Clusters of many atoms that act as tiny magnets in a material MAINODS3. A region around a magnet SFILEDGENAMICT4. Imaginary lines that represent magnetic field SLIENSOFGENTMICFOECR5. Materials that are strongly attracted to magnet GENTAMICORREF6. Materials that are repelled by magnet GENTAMICIAD7. Materials that are slightly attracted by magnet GENTAMICARAP8. A substance that possesses magnetic properties NETGAM9. Iron and other elements can become strongly magnetized NETGAMITAZIONT10. A magnet has two SLOPES Key to answers on page 33 14

Lesson 3 Electromagnetism What did you do today? Did you listen to a recorder? Did you use or hear a motor atwork in a mixer, blender, refrigerator, washing machine, hair dryer, fan, and vacuumcleaner? Did you hear a buzzer or doorbell sound? What about a cellular phone? If you saw or heard these devices or machines, you observed the combined effects ofelectricity and magnetism at work. Scientists learned how to use the relationship betweenelectricity and magnetism to produce electric currents and to make machines that wouldmake these devices function. These scientists and inventors have made amazing changesin the way you live. Read this lesson and you will appreciate the convenience of life because of electricityand magnetism. A. Electricity Makes Magnetism On the morning of February 16, 1820, an important discovery was made by accident. Professor Hans Christian Oersted in Denmark was giving a lecture on electricity to his students. He closed a switch to demonstrate the flow of current. There happened to be a compass nearby. Every time the professor closed the switch, the compass needle turned. Oersted had discovered that an electric current is surrounded by a magnetic field. Hans Christian Oersted His discovery made him conclude that a current- carrying wire produces a magnetic field. This led to the principle of electromagnet. An electromagnet is a magnet that can be switched on and off. It is a solenoid with a core. The strength of an electromagnet can be made stronger by increasing the number of turns on the core. 15

B. Magnetic Field and Electric Current Shortly after Oersted’s discovery that electricity produces magnetic field, scientistsexperimented with the opposite possibility. In 1831, Michael Faraday, an English scientist,discovered that a moving wire through a magnetic field could cause an electric current. Atabout the same time, an American scientist named Joseph Henry made a similardiscovery. A current produced by a magnetic field is an induced current. What you will do Activity 3.1 Make your own electromagnetMaterials: Large nail, copper wire, dry cell and paper clipsProcedure: 1. Gather all the materials needed. 2. Wrap the copper wire around the large nail. 3. Connect the free ends of the wire to a dry cell. 4. Place the iron nail coil near pieces of nail, paper clips and pins. 5. Observe what happens. ______________________________ 6. Disconnect the wire from the dry cell. What happens? ________________ Key to answers on page 33 16

What you will do Activity 3.2 Diagram AnalysisThe set up shows a wire that is bent and the ends were attached to a galvanometer. Diagram A Diagram BIn diagram A, the coil is moved down the space between the north and south poles (seearrow) of the two magnets. What happens to the galvanometer needle?_________________________________________________________________________In diagram B, the coil is moved up the space between the north and south poles (see arrow)of the two magnets. What happens to the galvanometerneedle?__________________________________________________________________If a galvanometer is an instrument used to measure very small electric currents, what isproduced by the coil of wire inserted between the poles of the magnet?_________________________________________________________________________Discussion This experiment showed that electricity is produced in a wire as it moves through amagnetic field. It also shows that the direction in which the coil moves affects the direction ofthe current. The conducting material like the coil cuts the magnetic lines of force thatproduce electric current. If we moved the magnet in and out of the magnetic field, is there a currentproduced? Yes, the effect is the same, but if the magnet does not move, no current isproduced, because no magnetic lines of force exist. Key to answers on page 33 17

Michael Faraday concluded that when a wire is moved through a magnetic field, a current is generated in the wire. This process of generating current by the relative motion between a wire and magnetic field is called electromagnetic induction. Michael FaradayApplications of Electromagnetic InductionWhat is the difference between the generator and a motor?1. What is a generator? A generator operates on the principle of electromagnetic induction. A generator is adevice that converts mechanical energy to electrical energy. It consists of a u-shapedmagnet that produces magnetic field, and insulated loop of wire. The wire loop is attached toa power source placed between the magnetic poles. The power source slowly begins torotate the wire clockwise. As the wire loop moves, it cuts through the magnetic lines of forcethat induce current. As the rotation of the wire loop continues, it moves parallel to themagnetic lines of force. When the wire is in this position, no lines of force are cut, therefore,there is no electricity. As it moves further clockwise, the lines of force are cut againproducing electricity. The alternate movement of the wire causes alternating current. Arectifier changes alternating current into direct current. MAGNET COIL COMMUTATORBRUSHES SHAFT 18