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Physics....

I'm really stuck on Q14 from the PHYA4 section A paper.

I'm self teaching - so any helpful videos you could link me too would be massively helpful, as i really don't think i understand the concepts of electric potential and field lines :frown:

The question says that a charged particle moving in an electric field:

A) No work is done when the particle moves along a field line

B) No force acts on a charged particle when it moves along a field line

C) No work is done when a charged particle moves along a line of constant potential

D) No force acts on a charged particle when it moves along a line of constant potential.

The answer is C, is this because the electric potential difference accelerates the particle along the line?
But if work done = Force x distance moved, why is Work Zero? The force acting on the charged particle must be zero which i don't understand as its in an electric field :frown:

Reply 1

Stonebridge

Original post by physicso

Firstly there will always be a force on the charged particle when it is in the field. That's the definition of a field.
Work is done when the force moves the object in the direction of the force. (Or at least it moves so that it has some component of its motion in the direction of the field.) So if the particle moves at right angles to the field (the force lines) then the field does no work on the charge.

Potential in an electric field actually measures work done. If a charge moves to a place with a different potential in the field, work has been done.

If the charge moves along a line of constant potential then its potential is not changing. If it isn't changing then its constant. Constant potential means no change in energy. No change in energy implies no work done.
If you want to think in terms of the force, then no work is done when the charge moves at right angles to the force. The equipotential lines in a force field are always at right angles to the field lines.