A question about Magnetic Fields and A Charge

1. Apr 11, 2008

Hevonen

[SOLVED] A question about Magnetic Fields and A Charge

A charged particle enters in 90 degrees to the magnetic field i.e. the force on the charge is F = qvB as sin (angle) = 1. The question is which are the effects on the kinetic energy and momentum of the particle?

Alternatives:

A. KE => Changed
Momentum => Changed

B. KE => Unchanged
Momentum => Changed

The solution is B but I do not why? Please, help me.

2. Apr 11, 2008

Barny

I think...

As the force is perpendicular to the displacement no work (W=fxcos(angle)) will be done. It's kinetic energy, a scalar, remains unchanged.

However, the force does accelerate the charged particle. This acceleration is perpendicular to it's velocity. The momentum vector changes in direction, not magnitude.

Does this help?

3. Apr 11, 2008

Hevonen

In other words, the particle will circle around and around again ie it is not actually progressing anywhere. It stays where it is and circles. Hence, can it be said that there is no work done ie. KE is unchanged?

4. Apr 11, 2008

Barny

Yes I believe so.

5. Apr 11, 2008

Hevonen

Thanks! I think I understood :)

Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?