Question

Starting with a sample of pure $66Cu,\frac{7}{8}$ of it decays into Zn in 15 min. The corresponding half-life is.

• A. 5 min
• B. $7\frac{1}{2}$ min
• C. 10 min
• D. 15 min

Answer 1

Answer: (A)

5 min

Answer 2

$\frac{7}{8}$part decays i.e. remaining part is $\frac{1}{8}$.

$N = N_{0}\left( \frac{1}{2} \right)^{\frac{t}{T_{1/2}}} \Rightarrow \frac{1}{8} = \left( \frac{1}{2} \right)^{\frac{15}{T_{1/2}}} \Rightarrow T_{1/2}$=5 min.