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Question: The count rate of a Geiger- Muller counter for the radiation of a radioactive material of half life ...

The count rate of a Geiger- Muller counter for the radiation of a radioactive material of half life of 30 minutes decreases to 5s1s^{- 1}after 2 hours. The initial count rate was.

A

25s1s^{- 1}

B

80s1s^{- 1}

C

625s1s^{- 1}

D

20s1s^{- 1}

Answer

80s1s^{- 1}

Explanation

Solution

A=A0(12)t/T1/2A = A_{0}\left( \frac{1}{2} \right)^{t/T_{1/2}}5=A0(12)2×6030=A0165 = A_{0}\left( \frac{1}{2} \right)^{\frac{2 \times 60}{30}} = \frac{A_{0}}{16}A0=80sec1A_{0} = 80sec^{- 1}