Question regarding electromagnetic interaction

[Lory73]

Hello
I attach a question (PDF-file) which I found in an old physics book, I printed the question and re-generated the drawing which were a bit hard to scan.

Can anyone answer the attached question, I think I know the answer but I want to be sure.

Thanks

Lory

 

[jtbell]

Tell us what you think the answer is, and your reasoning, and then we can either confirm it or rip it to shreds.

 

[Lory73]

Well, the obvious answer is that the plate experience a force downward.
The thing that puzzles me is whether the accelerated electrons are suppose to generate an ossilating electric field to both diretions (up and down) or a unidirectional electric field due to the fact that they are only accelerated in one direction.

Now, am I right ?

 

[pam]

There will be a non-oscillating electric field E_a in the direction of the acceleration, exerting a downward force on the positively charged plate, as you say.
There will also be an electric field E_b pointing toward the electron, which would exert a leftward force on the plate. E_a falls off as 1/r, while E_b falls off as 1/r^2, so each will dominate at different distances.
An oscillating charge radiates an oscillating field, but this charge is not oscillating.

 

[Lory73]

Thanks Pam