Which force field can accelerate an electron, but never change its speed?

1 Answer
Aritra G.
May 30, 2015

Magnetic force on a charge is given from the Lorentz force formula as :

F=qvBSin theta

As we see, the force always acts perpendicular to the initial velocity vector and as a result doesn't modify it's magnitude (speed) but, only changes it's direction. (The particle tends to revolve along a circle if theta = pi/2 or in a helical trajectory if other wise. The force vanishes when theta = 0.

Thus, it is the magnetic force which never changes the speed of a charged particle.

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