Modern Physics 5 Question 1
1. Half lives of two radioactive nuclei and are 10 minutes and 20 minutes, respectively. If initially a sample has equal number of nuclei, then after
60 minutes, the ratio of decayed numbers of nuclei
(Main 2019, 12 April II)
(a)
(b)
(c)
(d)
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Answer:
Correct Answer: 1. (d)
Solution:
- For substance
, half-life is , so it decays as
Similarly, for substance
So, number of nuclei of
Hence, ratio of decayed nuclei of
Alternate Solution
Number of active nuclei remained after
where,
So, for nuclei
Similarly, for nuclei