Tamil Nadu 10th Standard Science Book Solution | Lesson 6 – NUCLEAR PHYSICS


NUCLEAR PHYSICS - Book Back Answer


I. Choose the correct answer

1. Man-made radioactivity is also known as __________.

  1. Induced radioactivity
  2. Spontaneous radioactivity
  3. Artificial radioactivity
  4. a & c

Ans ; a & c

2. Unit of radioactivity is __________.

  1. roentgen
  2. curie
  3. becquerel
  4. all the above

Ans ; all the above

3. Artificial radioactivity was discovered by __________.

  1. Bequerel
  2. Irene Curie
  3. Roentgen
  4. Neils Bohr

Ans ; Irene Curie

4. In which of the following, no change in mass number of the daughter nuclei takes place

i) α decay     ii) β decay     iii) g decay     iv) neutron decay

  1. (i) is correct
  2. (ii) and (iii) are correct
  3. (i) & ( iv) are correct
  4. (ii) & (iv) are correct

Ans ; (i) & ( iv) are correct

5. __________ isotope is used for the treatment of cancer.

  1. Radio Iodine
  2. Radio Cobalt
  3. Radio Carbon
  4. Radio Nickel

Ans ; Radio Cobalt

6. Gamma radiations are dangerous because

  1. it affects eyes & bones
  2. it affects tissues
  3. it produces genetic disorder
  4. it produces enormous amount of heat

Ans : it produces genetic disorder

7. __________ aprons are used to protect us from gamma radiations

  1. Lead oxide
  2. Iron
  3. Lead
  4. Aluminium

Ans : Lead

8. Which of the following statements is/are correct?

i) α particles are photons    ii) Penetrating power of g radiation is very low

iii) Ionization power is maximum for α rays     iv) Penetrating power of g radiation is very high

  1. (i) & (ii) are correct
  2. (ii) & (iii) are correct
  3. (iv) only correct
  4. (iii) & (iv) are correct

Ans : (iii) & (iv) are correct

9. Proton – Proton chain reaction is an example of __________.

  1. Nuclear fission
  2. α – decay
  3. Nuclear fusion
  4. β – decay

Ans : Nuclear fusion

10. In the nuclear reaction 6X12 α decay ZYA, the value of A & Z.

  1. 8, 6
  2. 8, 4
  3. 4, 8
  4. cannot be determined with the given data

Ans : 4, 8

11. Kamini reactor is located at __________.

  1. Kalpakkam
  2. Koodankulam
  3. Mumbai
  4. Rajasthan

Ans : Kalpakkam

12. Which of the following is/are correct?

i) Chain reaction takes place in a nuclear reactor and an atomic bomb.
ii) The chain reaction in a nuclear reactor is controlled
iii) The chain reaction in a nuclear reactor is not controlled
iv) No chain reaction takes place in an atom bomb

  1. (i) only correct
  2. (i) & (ii) are correct
  3. (iv) only correct
  4. (iii) & (iv) are correct

Ans : (i) & (ii) are correct

II. Fill in the blanks

1. One roentgen is equal to __________ disintegrations per second.

Ans ; 2.58 × 10–4

2. Positron is an __________.

Ans ; Elementary particle

3. Anemia can be cured by __________ isotope.

Ans ; Fe59

4. Abbreviation of ICRP __________.

Ans ; International Commission on Radiological Protection

5. __________ is used to measure exposure rate of radiation in humans.

Ans ; Roentegen

6. __________ has the greatest penetration power.

Ans ; γ–rays

7. ZYAZ+1YA + X ; Then, X is __________.

Ans ; beta

8. ZXAZYA This reaction is possible in __________ decay.

Ans ; γ

9. The average energy released in each fusion reaction is about __________ J.

Ans ; 3.84 × 10–12

10. Nuclear fusion is possible only at an extremely high temperature of the order of __________ K.

Ans ; 107 to 109

11. The radio isotope of __________ helps to increase the productivity of crops.

Ans ; Phosphorus 32

12. If the radiation exposure is 100 R, it may cause __________.

Ans ; fatal diseases like leukemia

III. State whether the following statements are true or false: If false, correct the statement

1. Plutonium -239 is a fissionable material. ( True )

2. Elements having atomic number greater than 83 can undergo nuclear fusion. ( False )

  • Elements having atomic number lesser than 83can undergo nuclear fusion.

3. Nuclear fusion is more dangerous than nuclear fission. ( False )

  • Nuclear fission is more dangerous than Nuclear fusion.

4. Natural uranium U-238 is the core fuel used in a nuclear reactor. ( False )

  • Natural plutonium is the core fuel used in a nuclear reactor.

5. If a moderator is not present, then a nuclear reactor will behave as an atom bomb. ( True )
6. During one nuclear fission on an average, 2 to 3 neutrons are produced. ( True )
7. Einstein’s theory of mass energy equivalence is used in nuclear fission and fusion. ( True )

IV. Match the following

Match: I

a. BARCKalpakkam
b. India’s first atomic powerApsara station
c. IGCARMumbai
d. First nuclear reactor in IndiaTarapur
Ans ; a – 3, b – 4, c – 1, d – 2

Match: II

a. Fuellead
b. Moderatorheavy water
c. Control rodscadmium rods
d. Shielduranium
Ans ; a – 4, b – 2, c – 3, d – 1

Match: III

a. Soddy FajanNatural radioactivity
b. Irene CurieDisplacement law
c. Henry BequerelMass energy equivalence
d. Albert EinsteinArtificial Radioactivity
Ans ; a – 2, b – 4, c – 1, d – 3

Match: IV

a. Uncontrolled fission reactionHydrogen Bomb
b. Fertile materialNuclear reaction
c. Controlled fission reactionBreeder reactor
d. Fusion reactionAtom bomb
Ans ; a – 4, b – 3, c – 2, d – 1

Match: V

b. I – 131Age of fossil
b. Fertile materialFunction of Heart
c. Na – 24Leukemia
d. C – 14Thyroid disease
Ans ; a – 3, b – 4, c – 2, d – 1

V. Arrange the following in the correct sequence:

1. Arrange in descending order, on the basis of their penetration power

Alpha rays, beta rays, gamma rays, cosmic rays

Ans ; Gamma rays, Beta rays, Alpha rays, Cosmic rays.

2. Arrange the following in the chronological order of discovery

Nuclear reactor, radioactivity, artificial radioactivity, discovery of radium.

Ans ; radioactivity, Discovery of radium, artificial radioactivity, Nuclear reactor.

VI. Use the analogy to fill in the blank

1. Spontaneous process : Natural Radioactivity, Induced process : __________.

Ans ; Artificial Radioactivity

2. Nuclear Fusion : Extreme temperature, Nuclear Fission : __________.

Ans ; Low Temperature

3. Increasing crops : Radio phosphorous, Effective functioning of heart : __________.

Ans ; Radio sodium

4. Deflected by electric field : α ray, Null Deflection : __________.

Ans ; γ rays

VII. Numerical problems:

1. 88Ra226 experiences three α – decay. Find the number of neutrons in the daughter element.

132 Neutrons.

2. A cobalt specimen emits induced radiation of 75.6 millicurie per second. Convert this disintegration in to becquerel (one curie = 3.7 × 1010 Bq)

2797200000 becquerel = 75.6 millicurie.

VIII. Assertion and reason type questions:

Mark the correct choice as

  1. If Both the assertion and the reason are true and the reason is the correct explanation of assertion.
  2. Both the assertion and the reason are true, but the reason is not the correct explanation of the assertion.
  3. Assertion is true, but the reason is false.
  4. Assertion is false, but the reason is true.

1. Assertion: A neutron impinging on U235, splits it to produce Barium and Krypton.

Reason: U – 235 is a fissile material.

  • a) Both the assertion and the reason are true and the reason is the correct explanation of the assertion

2. Assertion: In a β – decay, the neutron number decreases by one.

Reason: In β – decay atomic number increases by one.

  • a) Both the assertion and the reason are true and the reason is the correct explanation of the assertion

3. Assertion: Extreme temperature is necessary to execute nuclear fusion.

Reason: In a nuclear fusion, the nuclei of the reactants combine releasing high energy.

  • a) Both the assertion and the reason are true and the reason is the correct explanation of the assertion

4. Assertion : Control rods are known as ‘neutron seeking rods’.

Reason : Control rods are used to perform sustained nuclear fission reaction.

  • a) Both the assertion and the reason are true and the reason is the correct explanation of the assertion

IX. Answer in one or two word (VSA)

1. Who discovered natural radioactivity? 2K OOK

Henry Becquerel

2. Which radioactive material is present in the ore of pitchblende?


3. Write any two elements which are used for inducing radioactivity

Boron, Aluminium

4. Write the name of the electromagnetic radiation which is emitted during a natural radioactivity.

gamma radiation

5. If A is a radioactive element which emits an alpha particle and produces 104Rf259? write the atomic number and mass number of the element A.

106Sg263Atomic number of a = 106 ; Mass number of a = 263

6. What is the average energy released from single fission process?

The average energy released from a single process is 200MeV=3.2x 10-10 J

7. Which hazardous radiation is the cause for the genetic disease?

Gamma Radiation

8. What is the amount of radiation that may cause death of a person when exposed to it?

600 R.

9. When and where was the first nuclear reactor built ?

1942, Chicago,USA; 1956, Mumbai.

10. Give the SI unit of radioactivity


11. Which material protects us from radiation?


X. Answer the following questions in few sentences.

1. Write any three features of natural and artificial radioactivity.

Natural radioactivity:

  • Emission of radiation due to self-disintegration of a nucleus
  • Exhibited by elements with atomic number more than 83
  • This cannot be controlled

Artificial radioactivity:

  • Emission of radiation due to disintegration of a nucleus through induced process.
  • Exhibited by elements with atomic number less than 83
  • This can be controlled

2. Define critical mass.

  • The minimum mass of fissile material necessary to sustain the chain reaction is called critical mass.
  • It depends on the nature, density and the size of the fissile material.

3. Define one roentgen.

It is the quantity of radioactive substances which produces a charge of 2.58x 10-4 coulombs in 1 kg of air under standard conditions of pressure, temperature and humidity.

4. State Soddy and Fajan’s displacement law.

  • When a parent element emits an alpha particle the new element is formed with a decrease in atomic number by two and mass number by four.
  • When a parent nucleus emits a beta particle the daughter nucleus is formed with an increase in atomic number by one and has same mass number of the parent nucleus.
  • In gamma decay, the energy level of nucleus only changes. No new elements are formed.

5. Give the function of control rods ina nuclear reactor.

  • The control rods are used to control the chain reaction as they are very good absorbers of neutrons.
  • By pushing in and pulling out, the reaction rate can be controlled.

6. In Japan, some of the new born children are having congenital diseases. Why?

  • The nuclear bomb dropped during World War II emitted gamma radiation.
  • Gamma rays caused injury to genes in the reproductive cells.
  • This gives rise to mutations which pass on from generation to generation.

7. Mr, Ramu is working as an X – ray technician in a hospital. But, he does not wear the lead aprons. What suggestion will you give to Mr. Ramu?

  • Radiation emitted by the X-ray machine can easily passes through our body and can cause genetic diseases.
  • These have been passed by genetic diseases from generation to generation.
  • When the emitted radiation is so high, it leads to death. So Mr. Ramu must wear the lead aprons.

8. What is stellar energy?

Fusion reaction that takes place in the cores of the Sun and other stars results in an enormous amount of energy, called stellar energy.

9. Give any two uses of radio isotopes in the field of agriculture.

  • To increase the productivity of crops
  • Remains fresh beyond their normal life time

XI. Answer the following questions in detail:

1. Explain the process of controlled and uncontrolled chain reactions.

a) Controlled chain reaction: 

  • In the controlled chain reaction the number of neutrons released is maintained to be one.
  • This is achieved by absorbing the extra neutrons with a neutron absorber leaving only one neutron to produce further fission.
  • Thus, the reaction is sustained in a controlled manner.
  • The energy released due to a controlled chain reaction can be utilized for constructive purposes.
  • Controlled chain reaction is used in a nuclear reactor to produce energy in a sustained and controlled manner.

b) Uncontrolled chain reaction:

  • In the uncontrolled chain reaction the number of neutrons multiplies indefinitely and causes fission in a large amount of the fissile material.
  • This results in the release of a huge amount of energy within a fraction of a second.
  • This kind of chain reaction is used in the atom bomb to produce an explosion.

Uncontrolled chain reaction

2. Compare the properties of alpha, beta and gamma radiations.

Propertiesα – rayβ-rayγ-ray
What are they?Helium nucleus (2He4) consisting of two protons and two neutrons.They are electrons (2He0), basic elementary particle in all atomsThey are electromagnetic waves consisting of photons
ChargePositively charged particles. Charge of each alpha particle = + 2eNegatively charged particles.Charge of each beta particle = -eNeutral particles. Charge of each gamma particle =  zero
Penetrating powerLow penetrating power (even stopped by a thick paper)Penetrating power is greater than that of α rays. They can penetrate through a thin metal foil.They have very high penetrating power greater than that of β rays. They can penetrate through thick metal blocks.
Effect of electric and magnetic fieldDeflected by both the fields. (in accordance with Fleming’s left-hand rule)Deflected by both the fields, but the direction of deflection is opposite to that for alpha rays (in accordance with Fleming’s left hand rule)They are not deflected by both the fields
SpeedTheir speed ranges from 1/10 to 1/20 time the speed of lightTheir speed go up to 9/10 times the speed of lightThey travel with the speed of light.

3. What is a nuclear reactor? Explain its essential parts with their functions.

  • A nuclear reactor is a device in which the nuclear fission reaction takes place in a self sustained and controlled manner.


  • A fissile material is used as the fuel.
  • The commonly used fuel material is uranium.


  • A moderator is used to slow down the high energy neutrons to provide slow neutrons.
  • Graphite and heavy water are the commonly used moderators.

Control rod:

  • Control rods are used to control the number of neutrons in order to have sustained chain reaction.
  • Mostly boron or cadmium rods are used as control rods. They absorb the neutrons.


  • Acoolant is used to remove the heat produced in the reactor core, to produce steam.
  • This steam is used to run a turbine in order to produce electricity.
  • Water, air and helium are some of the coolants.

Protection wall:

  • A thick concrete lead wall is built around the nuclear reactor in order to prevent the harmful radiations from escaping into the environment.



Schematic diagram of a nuclear reactor

XII. Higher Order Thinking Skills (HOTS)

1. Mass number of a radioactive element is 232 and its atomic number is 90. When this element undergoes certain nuclear reactions, it transforms into an isotope of lead with a mass number 208 and an atomic number 82. Determine the number of alpha and beta decay that can occur.

In alpha decay atomic number decreases by two and mass number decreases by four. So

232 – 208 = 24

Mass number decreased by 24. So 6 alpha particle would come out.

90X232  78Y208 + 6 2He4

In beta decay atomic number increases by one

78+4= 82

So, 4 beta particle would come out.

78 Y 208   82 Z 208 + 4 -1eo

So, six alpha particle and four beta particles would come out.

2. ‘X-rays should not be taken often’. Give the reason.

  • The intensity of radiation used in X-ray machine is small , so the chance that X-ray will cause severe problems is very low.
  • X-ray posses almost equal energy like gamma radiation.
  • So, if we take often, it may destructive living cell present in our body.
  • Tt may leads to cancer.

3. Cell phone towers should be placed far away from the residential area – why?

  • Cell phone companies are used non-ionised radiations.
  • Itis not harmful like X-ray or gamma radiation.
  • In 2006 report issued by the WHO, human body absorbs energy from cell phone towers which is almost five times more than FM and Television.
  • Signals from each mobile towers travels few miles from there.
  • The closer we are the greater the danger.


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