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Class XII

PHYSICS

Chapter-13-NUCLEI

WORKSHEET-4

1. The relation between half-life T1/2 of a radioactive sample and its mean life x is

2. The half-life of a radioactive nucleus is 3 hours. In 9 hours, its activity will be reduced to a factor
of

3. A radioactive element has half-life period 1600 years. After 6400 years what amount will remain?

A
4. A nucleus X emits an α-particle. The resultant nucleus emits a β-particle. The respective
Z
atomic and mass numbers of the daughter nucleus will be
(a) Z – 3, A – 4
(b) Z – 1, A – 4
(c) Z – 2, A – 4
(d) Z, A – 2
th
5. The half life of a radioactive susbtance is 30 days. What is the time taken to disintegrate to 3/4
of its original mass?
(a) 30 days
(b) 15 days
(c) 60 days
(d) 90 days
–
6
6. Complete the series 6He → e + Li +
(a) neutrino
(b) antineutrino
(c) proton
(d) neutron
7. Suppose we consider a large number of containers each containing initially 10000 atoms of a
radioactive material with a half-life of 1 year. After 1 year, [NCERT Exemplar]
(a) all the containers will have 5000 atoms of the material.
(b) all the containers will contain the same number of atoms of the material but that number will
only be approximately 5000.
(c) the containers will in general have different numbers of the atoms of the material but their
average will be close to 5000.
(d) none of the containers can have more than 5000 atoms.
8. When a nucleus in an atom undergoes a radioactive decay, the electronic energy levels of the
atom [NCERT Exemplar]