CUET · PHYSICS · PYQ PAPER 2025
A long straight wire of radius 'a' carries a steady current 'I'. The current is uniformly distributed across its area of cross-section. The ratio of magnitude of magnetic fields \( B_1 \) at a distance a/2 and \( B_2 \) at a distance 2a from the axis of the wire is :
- A 1 : 2
- B 1 : 1
- C 2 : 1
- D 4 : 1
Answer & Solution
Correct Answer
(B) 1 : 1
Step-by-step Solution
Detailed explanation
\( B_1 = \frac{\mu_0 I (a/2)}{2 \pi a^2} = \frac{\mu_0 I}{4 \pi a} \) \( B_2 = \frac{\mu_0 I}{2 \pi (2a)} = \frac{\mu_0 I}{4 \pi a} \) \( \frac{B_1}{B_2} = \frac{\mu_0 I / (4 \pi a)}{\mu_0 I / (4 \pi a)} = 1 : 1 \)
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