1.

The radioactivity of given sample of whisky due to tritium (half life = 12 yrs) was found to be only 3.125% of that measured in a recently purchased bottle marked "10 yrs old". By how many years ago sample must have been prepared ?

Answer»

20 yrs
30 yrs
50 yrs
70 yrs

Solution :`A/A_(0)=(1/2)^(t/T) rArr (3.125)/(100) =(1/2)^(t/T)`
`rArr (1)/(32)=(1/2)^(t/T) rArr (1/2)^(5) =(1/2)^(t/T)`
`t=5T =5 XX 12=60yrs`
TOTAL AGE of sample `=60+10=70yrs`


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