In a radioactive disintegration, the ratio of initial number of atoms to the number of atoms present at time…

In a radioactive disintegration, the ratio of initial number of atoms to the number of atoms present at time $t=\frac{1}{2 \lambda}$ is $[\lambda=$ decay constant $]$
  1. $\frac{1}{\mathrm{e}}$
  2. $\sqrt{\mathrm{e}}$
  3. $\mathrm{e}$
  4. $2 \mathrm{e}$

Solution

According to radioactive disintegration law, $\begin{aligned} & \mathrm{N}=\mathrm{N}_0 \mathrm{e}^{-\lambda \mathrm{t}} \\ & \frac{\mathrm{N}}{\mathrm{N}_0}=\mathrm{e}^{-\lambda t} \\ & \frac{\mathrm{N}}{\mathrm{N}_0}=\mathrm{e}^{-\lambda \times \frac{1}{2 \lambda}} \\ & \left(\because t=\frac{1}{2 \lambda}\right) \\ & \frac{\mathrm{N}}{\mathrm{N}_0}=\mathrm{e}^{-\frac{1}{2}} \\ & \frac{\mathrm{N}_0}{\mathrm{~N}}=\mathrm{e}^{\frac{1}{2}} \\ & \frac{\mathrm{N}_0}{\mathrm{~N}}=\sqrt{\mathrm{e}} \\ & \end{aligned}$

Asked in: MHT CET 2023 (11 May Shift 1)

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