Page 1 - WS-3

Class XII

PHYSICS

Chapter-13-NUCLEI

WORKSHEET-3

4
–
1. An element A decays into an element C by a two step process A → B+ 2He 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
1
2+
+
4
–
2. The equation 41 H → 2 He + 2e + 26 MeV
represents
(a) β-decay
(b) γ-decay
(c) fusion
(d) fission
3. 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
4. In nuclear reaction, there is conservation of
(a) mass only
(b) energy only
(c) momentum only
(d) mass, energy and momentum
5. In nuclear reactors, the control rods are made of
(a) cadmium
(b) graphite
(c) krypton
(d) plutonium
6. Tritium is an isotope of hydrogen whose nucleus Triton contains 2 neutrons and 1 proton. Free
neutrons decay into p + e¯+v¯. If one of the neutrons in Triton decays, it would transform into
3
He nucleus. This does not happen. This is because [NCERT Exemplar]
3
(a) Triton energy is less than that of a He \ nucleus.
(b) the electron created in the beta decay process cannot remain in the nucleus.
(c) both the neutrons in triton have to decay simultaneously resulting in a nucleus with 3
3
protons, which is not a He nucleus.
(d) because free neutrons decay due to external perturbations which is absent in a triton
nucleus.
7. Heavy stable nuclei have more neutrons than protons. This is because of the fact that [NCERT
Exemplar]
(a) neutrons are heavier than protons.
(b) electrostatic force between protons are repulsive.
(c) neutrons decay into protons through beta decay.
(d) nuclear forces between neutrons are weaker than that between protons.
8. Sun’s radiant energy is due to
(a) nuclear fission.
(b) nuclear fusion.
(c) photoelectric effect.