CUET · PHYSICS · PYQ PAPER 2023

A circular coil of 20 turns and radius 10 cm is placed in a uniform magnetic field of 0.10 T normal to the plane of the coil. If the current in the coil is 5 A . The total torque on the coil is :

A \(3.14 \times 10^{-3} Nm\)
B \(3.14 \times 10^{-2} Nm\)
C 3.14 Nm
D Zero

Verified Solution

Answer & Solution

Correct Answer

(D) Zero

Step-by-step Solution

Detailed explanation

\( \tau = NIAB \sin\theta \) \( \text{Since the magnetic field is normal to the plane of the coil, } \theta = 0^\circ \) \( \tau = (20)(5 \text{ A})(\pi (0.1 \text{ m})^2)(0.10 \text{ T}) \sin(0^\circ) \) \( \tau = 0 \text{ Nm} \)

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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Match List-I with List-II

List-I (Optical instrument)	List-II (Magnifying power)
(A) Magnifying power m of a simple microscope	(I) \( m = 1 + (D/f) \)
(B) Magnifying power m of a simple microscope if the image is at infinity	(II) \( m = (L/f_0) \times (D/f_e) \)
(C) Magnifying power m of a compound microscope	(III) \( m = f_0 / f_e \)
(D) Magnifying power m of a telescope	(IV) \( m = D/f \)

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(A) \( X_{red} \)
(B) \( X_{blue} \)
(C) \( X_{green} \)
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Match List-I with List-II

List-I	List-II
(A) Magnifying power of a simple microscope	(I) \( \frac{L}{f_o} \times \frac{D}{f_e} \)
(B) Magnifying power of a compound microscope	(II) \( \frac{f_o}{f_e} \left(1 + \frac{f_e}{D}\right) \)
(C) Magnifying power of a telescope (normal adjustment)	(III) \( 1 + \frac{D}{f_e} \)
(D) Magnifying power of a telescope when final image is formed at least distance of distinct vision	(IV) \( \frac{f_o}{f_e} \)

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