In a radioactive material,the activity at time $t_1$ is $R_1$ and at a later time $t_2$ it is $R_2$. If the decay constant of the material is $\lambda$,then:

  • A
    $R_1 = R_2$
  • B
    $R_1 = R_2 e^{-\lambda(t_1 - t_2)}$
  • C
    $R_1 = R_2 e^{\lambda(t_1 - t_2)}$
  • D
    $R_1 = R_2 \left( \frac{t_1}{t_2} \right)$

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