Q. The count rate of $10g$ of radioactive material was measured at different times and this has been shown in the figure. The half life of material and the total counts (approximately) in the first half life period, respectively are
A) $4h,9000$
B) $3h,14000$
C) $3h,235$
D) $3h,50$
Explanation
(b) Read time for 50 count rate, it gives half life period of $3\ hrs$, one small square gives 600 counts $(10 \times 60)$. The number of small squares between graph and time axis are approx 24
Hence count rate $= 24 \times 600 = 14400$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.