Question

Derive an equation of magnetic field of a moving point charge.

Answer 1

The magnetic field vector B at point P at position vector r, from the charge q moving with a velocity vector v is found to be

Note down the following points regarding this equation. 

(a) Magnitude of B is,

It is zero at θ = 0º and 180º and maximum at θ = 90º

(c) Suppose a charge q₁ is moving with velocity and vector v₁ another charge q₂ is moving with velocity vector v₂ at position vector r relative to q₁, then force on q₂ will be,

This corresponds to Coulomb’s electrical force between the charges q₁ and q₂ moving with velocities vector v₁ and v₂ respectively relative to an observer at rest.