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CBSE Class 10 Answered

The half-life of a radioactive nuclei is 3 hours. In 9 hours its mass will be reduced by a factor of :- a.) 1/9    b.)1/27   c.) 7/8    d.)1/6   GIVE WITH PROPER STEPS
Asked by acv27joy | 07 May, 2018, 10:12: PM
answered-by-expert Expert Answer
Mass does not disappear and change. what is changing during the time is the number of nuclides undergoing radioactivity that keep on decreasing.
 
hapf life = 3 hours.
 
let original number of nuclides is N.
 
for first half-life (3 hours) the number of nuclides becomes (N/2). hence decayed nuclides = N/2.
for second half-life (6 hours cumulative) the number of nuclides becomes (1/2)(N/2) i.e. (N/4). hence decayed nuclides = N/2-N/4=N/4.
for third half-life (9 hours cumulative) the number of nuclides becomes (1/2)(N/4) i.e. (N/8). hence decayed nuclides = N/4-N/8=N/8.
 
hence total number of decayed nuclides = (N/2)+(N/4)+(N/8) = (7/8)N
Answered by Thiyagarajan K | 08 May, 2018, 10:38: AM

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