question_answer

Starting with a sample of pure\[^{66}Cu,\] 7/8 of it decays into Zn in 15 min. The corresponding half-life is     AIEEE  Solved  Paper-2005

A) 10 min  

B)        15 min  

C)        5 min    

D)        \[7\frac{1}{2}\] min

Correct Answer: C

Solution :

The number of particles left undisintegrated, where,decay constant initial number of atoms andpresent number of atoms                      \[8={{e}^{\lambda \,t}}\] Taking log both sides, we get \[3\,\,\ln \,\,2=\lambda \,t\] Half life period