Question

A straight wire of diameter $0.5mm$ carrying a current of $1A$ is replaced by another wire of $1mm$ diameter carrying same current. The strength of the magnetic field far away is-

• A. Twice the earlier value
• B. Half of the earlier value
• C. Quarter of the earlier value
• D. No change

Answer 1

The correct option is D No change

magnetic field by wire $B=\frac{{\mu }_{0}I}{2\pi R}$ where $R$ is distance from the wire, (not radius) hence, for a change of diameter, with no change in current, the magnetic field remain unchanged.