Question

The counting rate of disintegration of radioactive source at $t=0$ second was $1600$ counts per second and at $t=8$ seconds was $100$ counts per second. The counting rate observed as counts per seconds, at $t=6$ second would have been

• A. $100$
• B. $200$
• C. $300$
• D. $400$

Answer 1

The correct option is B $200$

In $8sec$ count is $100$

So, $2^n=\frac{1600}{100}$

$n=4$, so in 8 sec there are four half lifes,half life is $2sec$

In $6sec$ there are 3 half life, count after $6sec=$ $\frac{1600}{2^3}$$=200$