Effect on electron in magnetic field

[xiangyu7]

Here's a question that I'm quite confused about:

A uniform constant magnetic field is directed into the page. An electron of constant mass and charge follows a clockwise spiral of decreasing radius path. Is the particle spead increasing or slowing down? and Why?

 

[curly_ebhc]

try this

I see two forces here (sort of, one is a consequense of the other):

1st force (the real one): The electromagnetic force
Look at what you have:
B-field, velocity, charge (its an electron)

2nd force (implied in the motion): Centripital Force
What the first force is doing. Set the two equal. See what happens when you vary radius.

Don't forget Centripital force= mass x centripital acceleration



That should get you through the problem.

curly