CUET · PHYSICS · PYQ PAPER 2023

The half life of a radioactive isotope of Iodine 131 is 8 days. Starting with 64 mg of the Iodine 131, the amount that disintegrates in 24 days is :

A 8 mg
B 16 mg
C 32 mg
D 56 mg

Verified Solution

Answer & Solution

Correct Answer

(D) 56 mg

Step-by-step Solution

Detailed explanation

\(n = \frac{t}{T_{1/2}}\) \(n = \frac{24}{8} = 3\) \(N = N_0 (\frac{1}{2})^n\) \(N = 64 \text{ mg} (\frac{1}{2})^3 = 64 \text{ mg} \times \frac{1}{8} = 8 \text{ mg}\) \(\text{Amount disintegrated} = N_0 - N\)…

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

Same subject

'n' identical small drops are charged to V volt each. They coalesce to form a bigger drop. The potential of the bigger drop will be:

CUET 2025 Medium

Match List-I with List-II (Symbols have their usual meanings)

List-I (Physical Quantity)	List-II (Expression)
(A) Current density	(I) \( \frac{e E \tau}{m} \)
(B) Drift velocity	(II) \( \frac{n e^2 \tau}{m} \)
(C) Conductivity	(III) \( \frac{e \tau}{m} \)
(D) Mobility	(IV) \( n e v_d \)

Choose the correct answer from the options given below:

CUET 2025 Easy

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