Question

A steady current \(I\) flows through a long straight wire of radius \(a\). The current is uniformly distributed across its cross-section. The ratio of the magnetic fields due to the wire at distances \(\frac{a}{4}\) and \(3a\) respectively from the axis of the wire is:

• A. \(3:4\)
• B. \(4:3\)
• C. \(2:3\)
• D. \(1:4\)

Hint:

Inside a uniformly current-carrying wire, \(B\propto r\). Outside the wire, \(B\propto \frac{1}{r}\).

Answer 1

The Correct Option is A