-
A long straight wire of radius a carries a steady current I. The current is uniformly distributed over its cross-section. The ratio of the magnetic fields B and B', at radial distances a/2 and 2a respectively, from the axis of the wire is :
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- 1/4
- 1/2
- 1
- 4
Correct Option: C
For points inside the wire i.e., (r ≤ R)
| Magnetic field B = | ||
| 2πR² |
For points outside the wire (r ≥ R)
| Magnetic field, B’ = | ||
| 2πR |
| ∴ | = | = 1 : 1 | |||
| B | 2πa² | ||||
| B' | |||||
| 2π(2a) | |||||
