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?

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|= (μ0/4π) 2l/r
Where, μ0 = Permeability of free space = 4π x 10^-7 T m A^-1

|B|=  (4π x 10^-7 )/4π  x ( 2 x 35 )/0.2 = 3.5 x 10⁻⁵ T

Hence, the magnitude of the magnetic field at a point 20 cm from the wire is 3.5 x 10^–5 T.