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Physics · JEE | Moving Charges and Magnetism
हिन्दीReferring to the configuration shown in Figure 4.13 for a long straight wire of circular cross-section (radius \( a \)) carrying a uniform steady current \( I \), what is the ratio of the magnetic field at a distance \( r = \frac{a}{2} \) inside the wire to that at \( r = 2a \) outside the wire?
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Correct answer · Option D
1 : 1
Explanation
For \( r < a \), \( B = \frac{\mu_0 I r}{2\pi a^2} \). At \( r = a/2 \), \( B = \frac{\mu_0 I}{4\pi a} \). For \( r > a \), \( B = \frac{\mu_0 I}{2\pi r} \). At \( r = 2a \), \( B = \frac{\mu_0 I}{4\pi a} \). Their ratio is 1 : 1.
