Question

The radioactivity of a sample is X at time $t_1$ and Y and a time $t_2$. If the mean life time of the specimen is $\tau$, the number of atoms that have disintigrated in the time interval $t_1-t_2$ is

• A. $X{t}_1-Y{t}_2$
• B. $X-Y$
• C. $\frac{X-Y}{\tau }$
• D. $(X-Y)\tau$

Answer 1

The correct option is D $(X-Y)\tau$

$X=\lambda N_{1}Y=\lambda N_2{N}_1-N_2=\frac{X-Y}{\lambda }=(X-Y)\tau$