Question

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

• A. twice the earlier value
• B. same as the earlier value
• C. one - half of the earlier value
• D. one - quarter of the earlier value

Answer 1

Answer: (B)

The magnetic field due to a current carrying straight wire at distance $a$ is given by
$B=\frac{\mu _{0} I}{2 \pi a}$
So, $B \propto I$
The current is same in both the wires, hence magnetic field strength will also be the same.