Question

The decay constant of a radioactive isotope is `lambda`. If `A_1` and `A_2` are its activites at time `t_1` and `t_2` respectively, then the number of nuclei which have decayed the time `(t_1-t_2)`
A. `A_1t_1-A_2t_2`
B. `A_1-A_2`
C. `(A_1-A_2)//lambda`
D. `lambda(A_1-A_2)`

Answer 1

Correct Answer - c
`A_1=lambdaN_1` at time `t_1`
`A_2=lambdaN_2` at time `t_2`
Therefore, number of nuclei decayed during time interval `(t_1-t_2)` is `N_1-N_2=((A_1-A_2))/lambda`