Question

Distinguish between the forces experienced by a moving charge in a uniform electric field and in a uniform magnetic field. (Any two points)

Answer 1

Sr. No.	Force on a charge moving in a uniform electric field `vec E`	Force on a charge moving in a uniform magnetic field `vec B`
1.	The magnitude of the electric force is directly proportional to the magnitudes of the charge and the field, Fe = |q| E.	The magnitude of the magnetic force is directly proportional to the magnitudes of the charge, velocity, magnetic field and the sine of the smaller angle θ between `vec v` and `vec B`, Fm = |q| v B sin θ.
2.	The direction of the force on the charge, and the resulting acceleration, depend on the sign of the charge: in the direction of `vec E` if q is positive and opposite to `vec E` if q is negative.	The direction of the force, and the resulting acceleration, depend on the sign of q and are perpendicular to both `vec v` and `vec B`: in the direction of `vec v xx vec B` if q is positive and opposite to `vec v xxvec B` if q is negative.
3.	The electric force acts on the charge independent of whether the charge is stationary or moving.	The magnetic force acts only on a moving charge and is zero if |`vec v`| = 0 or if `vec v` is parallel or antiparallel to `vec B`.
4.	The work done by the electric force is not zero and changes the kinetic energy of the charge.	For Fm ≠ 0, `vec(F)_m` is centripetal and the work done by it is zero at every instant so that it cannot change the kinetic energy of the charge.