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Question: A and B are two radioactive substances whose half lives are 1 and 2 years respectively. Initially 10...

A and B are two radioactive substances whose half lives are 1 and 2 years respectively. Initially 10 gm of A and 1 gm of B is taken. The time (approximate) after which they will have same quantity remaining is –

A

6.62 years

B

5 years

C

3.2 years

D

7 years

Answer

6.62 years

Explanation

Solution

MA= MB Ž 102t/1\frac { 10 } { 2 ^ { t / 1 } } = 12t/2\frac { 1 } { 2 ^ { t / 2 } } Ž 2t/2 = 10

log10 2 t/2 = log10 10 Ž t2\frac { \mathrm { t } } { 2 } log10 2 = 1

t = 2log102\frac { 2 } { \log _ { 10 } 2 } = 6.62 years