Question

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

• A. unchanged
• B. quarter of its earlier value
• C. half of the earlier value
• D. twice the earlier value

Answer 1

The correct option is A unchanged

magnetic field due to straight wire carrying current $i$ at distance $x$ is given as

$B=\frac{{\mu }_{0}i}{2\pi x}$

so $B$ does not depends on the diameter of wire.

$B$ is unchanged