Electromagnetism Question (1 Viewer)

[SB257426]

I am stuck on this module 6 electromagnetism question:

'Two charged parallel plates have a potential difference of 35.0 V.

How far apart must these two plates be so that a point charge of -4.0*10^-8 C with a mass of 2.5*10^-6 kg will be exactly suspended against gravity?"

I dont have a diagram but the top plate was positive and the bottom plate was negative.

Cheers.

 

[wizzkids]

This question is fairly straightforward. It is modelled on the Millikan Oil Drop experiment.
(If you don't know what the Millikan Oil Drop experiment was, you better go look it up).
Examine the following diagram. The negatively charged particle "P" experiences an upwards force (the blue vector) from the electric field, and a downwards force (the green vector) from gravity. The particle will be suspended when these forces are equal and opposite. Our task is to determine the value of "d".
Do you think you can finish the problem now?

 

[howcanibesmarter]

Millikan oil drop is module 8, so maybe thats why you don't know. But using F=qE and F=mg, equating it and making d the subject (E=V/d), you get d=qV/mg. Subbing in known values should get you the correct answer.

 

[SB257426]

Millikan oil drop is module 8, so maybe thats why you don't know. But using F=qE and F=mg, equating it and making d the subject (E=V/d), you get d=qV/mg. Subbing in known values should get you the correct answer.

I did do that when I first tried the problem but I kept on getting the wrong answer.. thats why I posted it.... incase my reasoning to the formula was incorrect