JEE Main · 2022 · 28 Jul 2022 · Shift 1 · Modern Physics

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A freshly prepared radioactive source of half life 2 hours 30 minutes emits radiation which is 64 times the permissible safe level. The minimum time, after which it would be possible to work safely with source, will be ____ hours.

Answer: 15

Solution

The activity must reduce by a factor of 64, i.e.,

A = \frac{A _{0}}{64} = A_{0} \times 2^{- n}

, where

n = 6

half-lives. Time =

6 \times 2.5 = 15

hours.

JEE Main · 2022 · 28 Jul 2022 · Shift 1 · Integer answer

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