I Slowing down a moving electric charge

[Alex Schaller]

If an electric charge q is moving with a certain velocity v and we want to slow it down, this can only be done with an electrical force because magnetic force is perpendicular to displacement, correct? (watch video, time stamp 0:42)
video

 

[weirdoguy]

Yes. Although i see no video.

 

[PeroK]

Yes. Although i see no video.

It was only a pop video after all!

 

[weirdoguy]

Yes, I am thankful for whatever made it disappear.

Anyways, I wanted to write something in my first post, but I didn't, so I'll add it in this one, so that it's not completly useless:

force is perpendicular to displacement

This is true, but since this displacement is infinitesimal, I think that it is better to think in terms of velocity. Force is perpendicular to velocity at every instant, so it does not transfer energy, since it's power (scalar product of force and velocity) is zero. In general, keeping track of powers is easier than works done by forces.

I don't like infinitesimals.

 

[Gavran]

The velocity of an electric charge is a vector quantity and it can be changed by a magnetic force.

 

[weirdoguy]

The direction can be changed. OP talked about slowing down, which means readucing magnitude of velocity, which can't be done by magnetic field.