Homework Help: Physics - Potential difference (check + help)

Posted by Anonymous on Wednesday, October 13, 2010 at 5:15am.

A pair of horizontal plates are situated in a vacuum and separated by a distance of 1.8cm. What potential energy would need to be connected across the plates in order to hold a single electron suspended at rest between them?

Ans:
I used the formula
(qv)/d = mg ; where q=is the charge on the electron, d is the distance in metres; m is the mass and g is the gravitational constant on earth.

i get 1.00540...*10^-12

is this the correct answer??

Physics - Potential difference (check + help) - drwls, Wednesday, October 13, 2010 at 6:49am
Your equation is correct.
You do not provide any dimensions to go with your number. I would mark it incorrect for that reason alone.

Also, I assume that they are asking for a potential difference (energy per charge in Volts or J/C, not a potential energy. They are not the same thing.

V = m g D/e = 9.8*10^-31 kg*9.8m/s^2*0.018 m/1.6*10^-19 C
= 1.1*10^-12 Volts

You were on the right track; we nearly agree on the number. I did not keep many significant figures.

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