A) 3 hours
B) 6 hours
C) 2 hours
D) 8 hours
Correct Answer: A
Solution :
: For safe working, the intensity must reduce to 1/32. \[\therefore \] \[\frac{N}{{{N}_{0}}}={{\left( \frac{1}{2} \right)}^{t/T}}\] \[\Rightarrow \] \[\frac{1}{32}={{\left( \frac{1}{2} \right)}^{t/T}}\] Or \[{{\left( \frac{1}{2} \right)}^{5}}={{\left( \frac{1}{2} \right)}^{t/T}}\]\[\Rightarrow \] \[\frac{t}{T}=5\Rightarrow t=5T\] \[t=\frac{5\times 1}{2}=2.5\]hours Minimum time = 3 hours.
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