CUET · PHYSICS · PYQ PAPER 2025

A very long straight wire carries a current (I) directed along positive Y-axis. A point charge +Q moves with velocity (v) along X -axis. The direction of force on the charge at point (5,0,0) m is

A along positive x-axis
B along positive y-axis
C along negative z-axis
D along positive z-axis

Verified Solution

Answer & Solution

Correct Answer

(B) along positive y-axis

Step-by-step Solution

Detailed explanation

Direction of \(\vec{B}\) at (5,0,0) due to current along +Y (RHR): \(-\hat{k}\) (along negative z-axis). Direction of \(\vec{F} = q(\vec{v} \times \vec{B})\): \(+\hat{i} \times (-\hat{k}) = -(\hat{i} \times \hat{k}) = -(-\hat{j}) = +\hat{j}\). Direction of force is along…

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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