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Physics · PYQ NEET UG 2017
हिन्दीRadioactive material 'A' has decay constant \( 8\lambda \) and material 'B' has decay constant \( \lambda \). Initially they have same number of nuclei. After what time, the ratio of number of nuclei of material 'B' to that of 'A' will be \( \frac{1}{e} \)?
Correct answer · Option 2
\( \frac{1}{7\lambda} \)
Explanation
Given \( \frac{N_B}{N_A} = \frac{N_0 e^{-\lambda t}}{N_0 e^{-8\lambda t}} = e^{7\lambda t} = \frac{1}{e} = e^{-1} \implies 7\lambda t = -1 \) (time interval \( t = \frac{1}{7\lambda} \)).
