Question

Half life of a radioactive substance is 20 minute. Difference between points of time when it is 33% disintegrated and 67% disintegrated is approximately(a) 40 minute(b) 10 minute(c) 15 minute(d) 20 minute

Answer 1

Half life of a radioactive substance is 20 minute. Difference between points of time when it is 33% disintegrated and 67% disintegrated is approximately(a) 40 minute(b) 10 minute(c) 15 minute(d) 20 minute

Let say radio active element was = x

when it is 33% disintegrated then left over radioactive = x - (33/100)x = 0.67x

When it is 67% disintegrated then left over radioactive = x - (67/100)x = 0.33x

disintegration from 0.67x to 0.33x  = 0.34x

% decay = 0.34x/0.67x = 50.7 %  ≅ 50% ( half decay)

Decay is close to half decay

Half life of radio active substance is 20 minute = Half Decay

so time for disintegration from 0.67x to 0.33x = 20 minutes

Difference between points of time when it is 33% disintegrated and 67% disintegrated is approximately = 20 mins

Option d is correct - 20 Mins