CUET · PHYSICS · PYQ PAPER 2023
A radioactive isotope phosphorous-32 has an initial activity \( 10 \mu \text{Ci} \) and has half life of \( 14 \text{ days} \). What is the activity of the source after \( 42 \text{ days} \) ?
- A \( 1.25 \mu \text{Ci} \)
- B \( 2.5 \mu \text{Ci} \)
- C \( 5 \mu \text{Ci} \)
- D \( 0.625 \mu \text{Ci} \)
Answer & Solution
Correct Answer
(A) \( 1.25 \mu \text{Ci} \)
Step-by-step Solution
Detailed explanation
\( n = t / T_{1/2} = 42 \text{ days} / 14 \text{ days} = 3 \) \( A = A_0 (1/2)^n = 10 \mu \text{Ci} \times (1/2)^3 \) \( A = 10 \mu \text{Ci} \times 1/8 = 1.25 \mu \text{Ci} \)
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