A long straight wire of radius a carries a steady current i . The current is uniformly distributed across its cross section. The ratio of the magnetic - Physics MCQ AIEEE 2007 2026 | ExamTest.live

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A long straight wire of radius a carries a steady current i . The current is uniformly distributed across its cross section. The ratio of the magnetic field at distance a /2 and 2 a from the axis is:

Solution & Step-by-step Explanation

The magnetic field B due to a long straight wire of radius a is:Inside the wire (r \leq a): B_{in} = \frac{μ _{0} i r}{2 π a ^{2}} At r = a /2 : B_{1} = \frac{μ _{0} i ( a /2 )}{2 π a ^{2}} = \frac{μ _{0} i}{4 πa} Outside the wire (r \geq a): B_{o u t} = \frac{μ _{0} i}{2 π r} At r = 2 a : B_{2} = \frac{μ _{0} i}{2 π ( 2 a )} = \frac{μ _{0} i}{4 πa} The ratio is \frac{B _{1}}{B _{2}} = \frac{μ _{0} i /4 πa}{μ _{0} i /4 πa} = 1 .

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A long straight wire of radius a carries a steady current i . The current is uniformly distributed across its cross section. The ratio of the magnetic field at distance a /2 and 2 a from the axis is:

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