Q. $10\ g$ of radioactive material of half-life 15 year is kept in store for 20 years. The disintegrated material is
A) $12.5\ g$
B) $10.5\ g$
C) $6.03\ g$
D) $4.03\ g$
Explanation
(c) Remaining material $N = \frac{N}{2^{t/T}}$
$\Rightarrow N = \frac{10}{(2)^{20/15}} = \frac{10}{2.51} = 3.96g$
So decayed material $= 10 - 3.96 = 6.04\ g$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.