Frank Solutions for Chapter 6.1 Radioactivity Class 10 Physics ICSE

Exercises


1. Name the three elementary particles present in an atom. Locate their positions.
Answer 
Atom consists of three elementary particles, neutrons, protons and electrons. Neutron and protons form the central part of atom called nucleus where electrons revolve around this central part in orbits called electronic orbits.

2. Define nucleus.
Answer 
Nucleus is central part of an atom which consist of elementary particles protons and neutrons.

3. What do you mean by
(i) Atomic number,
(ii) Mass number,
(iii) Atomic mass
Answer 
(i) Atomic number is the number of protons present in the nucleus. As number of protons is equal to the number of electrons so atomic number also gives the number of electrons in an atom.
(ii) Mass number is the sum of protons and neutrons present in the nucleus.
(iii) Atomic mass of element is the relative mass of its atom as compared to the mass of carbon atom taken as 12.

4. (a) State the penetrating range of α, β and γ radiations. 
(b) Give the relative ionizing power of  α, β and γ radiations.
Answer 
(i) The penetrating power of a particle is least. Penetrating power of β particles is less but 100 times more than that of a particle. Y radiations have maximum penetration power. They are 100 times more penetrating than β particles. 
(ii) Ionisation power of a particle is maximum. It is about 100 times more than that of β particles. Ionisation power of β particle is about 100 times more than that of Y radiations. Y radiations have least ionisation power. 

5. Which of the radiations  α, β and γ is similar to a beam of electrons ?
Answer 
β radiations are similar to a beam of electrons.

6. What are isotopes?
Answer 
The atoms of same elements having the same atomic number Z but different mass number A are called isotopes.

7. Do isotopes have same chemical or physical properties?
Answer 
Isotopes have same chemical properties but have different physical properties.

8. What are isobars?
Answer 
The atoms of different elements having same mass number but different atomic number are called isobars.

9. State two similarities and two dissimilarities between the γ- rays and x -rays. 
Answer 
Similarities:
  • Both γ-radiations and X-rays affect photographic plate, both travel with the speed of light.

Dissimilarities:

  • γ-radiations are obtained in emissions from the radioactive substances due to energy change in the nucleus of their atoms and X- rays are obtained when highly energetic cathode rays are stopped by a heavy metal target of high melting point.
  • γ-radiations have high penetration power but X-rays do not have have very high penetration power.


10. What happens to the position of an element in the periodic table when it emits a (i) β - particle, and (ii) γ - radiation? Give reasons for your answer.
Answer 
(i) p particles are negatively charged particles with negligible mass so when a element emits a β particle its mass remain same but atomic number decreases by 1 unit. So after emitting a β particle position of element would shift 1 unit left to the periodic table in same row.
(ii) γ radiations are uncharged and have no mass. So there is no change in atomic mass and atomic number of element emitting Y radiations and position of element remain same in periodic table. 

11. What happens to the atomic number of element when (i) An α-particle , (ii) β- particle, and (iii) γ-radiation is emitted ? 
Answer
(i) a particle is represented by 2He4  this means it contains 2 protons so after emitting a a particle atomic number of element would decrease by 2 unit.
(ii) β particle is represented by -1e°  after emitting a β particle atomic number of element would increase by 1 unit.
(iii) γ-radiations have no charge and no mass so after emitting a γ-radiation atomic number of element remain unchanged. 

12. What happens to the mass number of an element when (i) An α- particle, (ii) A β - particle, and (iii) γ -  radiation is emitted ? 
Answer 
(i) a particle is represented by 2He4 this means it contains 2 protons and 2 neutrons so mass of a particle is 4 unit. Thus after emitting a particle mass number of element would decrease by 4 unit. 
(ii) p particle is represented by -1e° so after emitting a β particle mass number of element would remain unchanged. 
(iii)Y radiations have no charge and no mass so after emitting a γ-radiation mass number of element remain unchanged. 

13. A radioactive source emits three types of radiations. Name them.
(i) Name the radiations which are charged.
(ii) Name the radiations which are most penetrating.
(iii) Name the radiations which travel with the speed of light.
(iv) Name the radiations which have the largest mass.
Answer 
A radioactive source emits three types of radiations These are a radiations, β radiations and Y radiations.
(i) a radiations and p radiations are charged radiations.
(ii) γ-radiations are most penetrating radiations.
(iii) γ-radiation travels with speed of light.
(iv) a radiations have largest mass. 

14. 'Radioactivity is a nuclear phenomenon'. Comment on this statement.
Answer 
Radioactivity is the spontaneous random emission of particles from within the nucleus of atom. Radiations are emitted from nucleus of atom thus radioactivity is a nuclear phenomenon.

15. What kind of change takes place in a nucleus when a β-particle is emitted ? 
Answer 
β particle is represented by -1e° after emitting a β particle atomic number of element would increase by 1 unit and mass number of element would remain unchanged.

16. In fig. 5 shows a mixed source S of alpha and beta particles in a thick lead container. The particles pass through a magnetic field in a direction perpendicular to the plane of paper (inwards as shown by x). State and show in the diagram how the particles get affected. 
Answer 
(i) Alpha particles are heavy in mass and are positively charged so they are deflected less by magnetic field and direction is upward which can be calculated by Fleming left hand rule.
(ii) Beta particles are negligible in mass so they are highly deflected by magnetic field and they are negatively charge particle so they are deflected in downward direction.
(iii) Gamma radiations have no mass and no charge so they are not deflected by magnetic field.

17. In fig. 6 shows a radioactive source S in a thick lead container . The radiations pass through an electric field between the plates P and Q. Complete the diagram to show the paths of α , β and γ radiations. 

Why is the source S placed in a thick lead container ? 
Answer 

(i) Alpha particles are heavy in mass and are positively charged so they are deflected less and are deflected towards-charged plate. 
(ii) Beta particles are negligible in mass so they are highly deflected by electric field and they are negatively charge particle so they are deflected towards positive charged plate. 
(iii) Gamma radiations have no mass and no charge so they are not deflected by electric field.
Source S is placed in thick lead container because it is radioactive substance and radiates. Thick walls of lead absorb all the radiation except radiation going straight outside towards opened end. Thus, thick walls help to reduce leakage of radiations outside. 


18. A nucleus of an element X which has the symbol 84X202 emits an alpha particle and then a beta particle. The final nucleus is bYa. Find a and b.
Answer 
Initially element is represented by a particle is represented by 2He4  this means it contains 2 protons and 2 neutron so mass  of a particle is 4 unit. Thus after emitting a particle mass number of element would decrease by 4 unit and atomic number of element would decrease by 2. 
So after emitting a particle  would become 
β particle is represented by -1e° after emitting a β particle atomic number of element would increase by 1 unit and mass number of element would remain unchanged. 
So after emitting a β particle
The daughter nucleus is represented by bya  .

19. The mass number (A) of an element is not changed when it emits _______.
Answer 
The mass number of an element is not changed when it emits β and γ radiations.

20. The atomic number of a radioactive element is not changed when it emits ______
Answer 
The atomic number of a radioactive element is not changed when it emits γ radiations. 
 
21. A radioactive nucleus ZXA first emits a beta particle and then an alpha particle to give the resulting nucleus QYP. What will be the values of P and Q in terms of A and Z ? 
Answer 


22. What are radioisotopes? State two uses of radioisotopes.
Answer 
Artificial radioactive substances can be produced by bombarding lighter nuclides with alpha particles, protons and neutron. The radioactive substances produces in this manner are called radioisotopes.
Radioisotopes can be used as:
  1. Rays from Radium produce satisfactorily improvement in skin diseases.
  2. Radioactive Sulphur S35 helps to study advantages and disadvantages of fungicides.

23. State three safety precautions that you would take while handling the radioactive substances.
Answer 
Following precautions should be taken while handling the radioactive substances.
  1. The sources should only be handled by the forceps provided and never touched by hand.
  2. They should never be pointed towards a person.
  3. Food should not be taken where the sources are being used, as it may be contaminated.
  4. Never smoke near a radioactive source.

24. Why should a radioactive substance not be touched by hand?
Answer 

Radioactive substances should not be touched by hands because radiation emitted by radioactive substances can cause burns, Leukemia, eye cataract, sterility or many other dangerous disease.
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