Question

A long wire carries a current of 20 A along the directed axis of a long solenoid. The field due to the solenoid is 4 mT. Find the field at a point 3 mm from the solenoid axis.

Answer 1

Magnetic field due to the long wire
B₁=μ₀I/2πb=4π•10⁻⁷•20/2•π•0.003=1.3•10⁻³ T
( B₁ is directed normal to the axis of solenoid)
B=sqrt(B₁²+B₂²) =sqrt{(1.3•10⁻³)²+(4•10⁻³)²} =4.2•10⁻³ T