Question

A long straight wire carries a current of 35 A. What is the magnitude of the field B at a point 20 cm from the wire?

Answer 1

Current in the wire, $I = 35 A$
Distance of a point from the wire, $r = 20\,cm = 0.2\,m$
Magnitude of the magnetic field at this point is given as:
$|B|= \frac{μ_0}{4π}. \frac{2l}{r}$
Where,
$μ_0$= Permeability of free space
$= 4π × 10^{–7} T m A^{–1}$
So,
$|B| =\frac{4π × 10^{–7}}{4π} × \frac{2 × 35}{0.2}$
$= 3.5× 10^{-5}\, T$
Hence, the magnitude of the magnetic field at a point 20 cm from the wire is $3.5× 10^{-5}\, T$.