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The magnetic field at a distance r from a long wire carrying current i is 0.4 tesla. The magnetic field at a distance 2r is
- 0.2 tesla
- 0.8 tesla
- 0.1 tesla
- 1.6 tesla
Correct answer: 0.2 tesla
Solution
The magnetic field due to a long straight current-carrying wire is inversely proportional to the distance from the wire, as given by B = μ₀i / (2πr). Doubling the distance (2r) reduces the field to half, so the field becomes 0.2 tesla.
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