# Physics class 12 chapter 13 Objective Questions

## Nuclei Objective Questions

1. An element A decays into an element C by a two step process A → B+ 2He4 and B → C + 2e. Then,

(a) A and C are isotopes

(b) A and C are isobars

(c) B and C are isotopes

(d) A and B are isobars

Answer: (a) A and C are isotops

2. Light energy emitted by star is due to

(a) breaking of nuclei

(b) joining of nuclei

(c) burning of nuclei

(d) reflection of solar light

Answer: (b) joining of nuclei

3. In nuclear reaction, there is conservation of

(a) mass only

(b) energy only

(c) momentum only

(d) mass, energy and momentum

Answer: (d) mass, energy and momentum

4. In nuclear reactors, the control rods are made of

(b) graphite

(c) krypton

(d) plutonium

5. The mass number of iron nucleus is 56 the nuclear density is

(a) 2.29 × 1016 kgm-3

(b) 2.29 × 1017 kgm-3

(c) 2.29 × 1018 kgm-3

(d) 2.29 × 1015 kgm-3

Answer: (b) 2.29 × 1017 kgm-3

6. Order of magnitude of density of uranium nucleus is

(a) 1020 kg m-3

(b) 1017 kg m-3

(c) 1014 kg m-3

(d) 1011 kg m-3

Answer: (b) 1017 kg m-3

7. The radius of a spherical nucleus as measured by electron scattering is 3.6 fm. What is the mass number of the nucleus most likely to be?

(a) 27

(b) 40

(c) 56

(d) 120

8. The half life of a radioactive susbtance is 30 days. What is the time taken to disintegrate to 3/4th of its original mass?

(a) 30 days

(b) 15 days

(c) 60 days

(d) 90 days

Answer: (c) 60 days

9. The number of beta particles emitted by a radioactive substance is twice the number of alpha particles emitted by it. The resulting daughter is an

(a) isomer of parent

(b) isotone of parent

(c) isotope of parent

(d) isobar of parent

Answer: (c) isotope of parent

10. During negative β-decay, an antineutrino is also emitted along with the emitted electron. Then,

(a) only linear momentum will be conserved

(b) total linear momentum and total angular momentum but not total energy will be conserved

(c) total linear momentum, and total energy but not total angular momentum will conserved

(d) total linear momentum, total angular momentum and total energy will be conserved

Answer: (d) total linear momentum, total angular momentum and total energy will be conserved

11. An electron emitted in beta radiation originates from

(a) inner orbits of atom

(b) free electrons existing in the nuclei

(c) decay of a neutron in a nuclei

(d) photon escaping from the nucleus

Answer: (c) decay of a neutron in a nuclei

12. Complete the series 6He → e– + 6Li+

(a) neutrino

(b) antineutrino

(c) proton

(d) neutron

13. Consider α and β particles and γ-rays each having an energy of 0.5 MeV. In the increasing order of penetrating power, the radiation are respectively

(a) α, β, γ

(b) α, γ, β

(c) β, γ, α

(d) γ β, α

Answer: (a) α, β, γ

14. Atomic number decreases with the emission of a particles from the nucleus :

(A) 1

(B) 2

(C) 3

(D) 4

15. Density of nucleus is about :

(A) 2.29 x 107 kg m-3

(B) 2.29 x 10-7 kg m-3

(C) 2.29 x 1017 kg m-3

(D) 2.29 x 10-17 kg m-3

Answer: (C) 2.29 x 1017 kg m-3

16. Which of the relations is correct for radioactive atom ?

(A) Half-life = Average life

(B) Half-life = 2 x Average life

(C) Half-life = 1.6931 x Average life

(D) Half-life = 0.6931 x Average life

Answer: (D) Half-life = 0.6931 x Average life

17. The equivalent energy of 1 g of substance is :

(A) 9 x 1013 J

(B) 6 x 1012 J

(C) 3 x 1013 J

(D) 6 x 1013 J

Answer: (A) 9 x 1013 J

18. X-ray was discovered by:

(A) Becqueral

(B) Marie curie

(C) Roengton

(D) Vanlaw

19. The order of nuclear density is :

(A) 103

(B) 1017

(C) 106

(D) None

20. If R is the radius and A is the mass of a nucleus then the graph of log R versus log A will be:

(A) A straight line

(B) A parabola

(C) An Ellipse’

(D) None of these

Answer: (B) A parabola

21. The time in which radioactive substance become half of its intial amount is called :

(A) average life

(B) half-life

(C) time-period

(D) decay constant

22. Mass is converted into energy according to the relation :

(A) E = mc2

(B) E = mgh

(c) E = 1/2 mc2

(D) E = mgh / c2

Answer: (A) E = mc2

23. Who discovered heavy Hydrogen ?

(A) Uray

(B) Thomson

(C) Mosley

(D) Fermi

24. Which of the following is not a mode of radioactive decay ?

(A) positron emission

(B) electron capture

(C) fusion

(D) alpha decay

25. Which one of the following has maximum penetraing power:

(A) X-rays

(B) cathode rays

(C) α-rays

(D) Y-rays