12th physics chapter 13: full solution, notes, MCQ, & free PDF | Bihar board

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

• • (a) cadmium
  • (b) graphite
  • (c) krypton
  • (d) plutonium

Answer: (a) cadmium

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

Answer: (a) 27

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

Answer: (b) antineutrino

bihar board 12th physics chapter 13 most mcq solution

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

Answer: (B) 2

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

Answer: (C) Roengton 

19. The order of nuclear density is :

• • (A) 10³
  • (B) 10¹⁷
  • (C) 10⁶
  • (D) None

Answer: (B) 10¹⁷

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

Answer: (B) half-life

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

Answer: (A) Uray 

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

• • (A) positron emission
  • (B) electron capture
  • (C) fusion
  • (D) alpha decay

Answer: (C) fusion

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

• • (A) X-rays
  • (B) cathode rays
  • (C) α-rays
  • (D) Y-rays

Answer: (D) Y-rays

26. Time during which the amount of radioactive substance becomes half of its initial amount is called.

• • (A) Average life
  • (B) Half life
  • (c) Decay constant
  • (D) Time period

Answer: (B) Half life

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