Practice portal › Moving Charges and Magnetism › Force on a Moving Charge
Asked in RS Academy GUJCET booklet · Lorentz force and work done
Idea: a particle gains energy only from a force that does work, that is, one with a component along the displacement.
Electric force: q⃗E has a fixed direction, so a charge moving along ⃗E is pushed forward through the whole displacement and gains energy qEd.
Magnetic force: q(⃗v×⃗B) is perpendicular to ⃗v, so ⃗F·⃗v=0 and the work done is zero at every instant.
A magnetic field can therefore bend the path and change the momentum, but it cannot change the speed.
So a charged particle gains energy from the electric field.
Reading this solution needs no sign-in. You only sign in to practise against the clock and keep your progress.
Practise this with a timer