Nuclei - Result Question 98
101. A radioactive sample with a half life of 1 month has the label : ‘Activity= 2 micro curies on 1-81991. What would be its activity two months earlier?
[1988]
(a) 1.0 micro curie
(b) 0.5 micro curie
(c) 4 micro curie
(d) 8 micro curie
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Answer:
Correct Answer: 101. (d)
Solution:
- (d) In two half lives, the activity becomes one fourth.
Activity on 1-8-91 was 2 micro-curie
$\therefore$ Activity before two months,
$4 \times 2$ micro-curie $=8$ micro curie
Activity of substance decreases as number of undecayed nuclei decreases with time.
Also, Activity $\propto \frac{1}{\text{ Half life }}$
