CUET · PHYSICS · PYQ PAPER 2023

Under the influence of a uniform magnetic field, a charged particle moves with a constant speed \( v \) in a circle of radius \( r \). The time period of the revolution of the particle :

A depends on v and not on r
B is independent of both v and r
C depends on r and not on v
D depends on both v and r

Verified Solution

Answer & Solution

Correct Answer

(B) is independent of both v and r

Step-by-step Solution

Detailed explanation

\(qvB = \frac{mv^2}{r}\) \(v = \frac{qBr}{m}\) \(T = \frac{2\pi r}{v}\) \(T = \frac{2\pi r}{\left(\frac{qBr}{m}\right)}\) \(T = \frac{2\pi m}{qB}\) The time period is independent of both \(v\) and \(r\).

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.

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List-I (Physical quantity)	List-II (Unit)
(A) Threshold frequency	(I) J
(B) Planck's constant	(II) V
(C) Work function	(III) 1/s
(D) Stopping potential	(IV) J s