Question 76: Magnetism and Matter

Question

A long straight wire of circular cross-section (radius a) is carrying steady current I. The current I is uniformly distributed across this cross-section. The magnetic field is

Accepted Answer

The magnetic field due to a current carrying wire can be calculated using Ampere's law. When the current is uniformly distributed across the cross-section of the wire, the situation will be different inside and outside the wire.
Inside the wire (r  a), all the current in the wire is enclosed, so the magnetic field decreases with increasing r. This is a result of the magnetic field lines spreading out as they move away from the wire.

Answer

uniform in the region $$r < a$$ and inversely proportional to distance $$r$$ from the axis, in the region $$r > a$$

Answer

zero in the region $$r < a$$ and inversely proportional to $$r$$ in the region $$r > a$$

Answer

directly proportional to $$r$$ in the region $$r < a$$ and inversely proportional to $$r$$ in the region $$r > a$$

Answer

inversely proportional to $$r$$ in the region $$r < a$$ and uniform throughout in the region $$r > a$$

Magnetism and Matter

A long straight wire of circular cross-section (radius a) is carrying steady current I. The current I is uniformly distributed across this cross-section. The magnetic field is

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