# Homework Help: Potential difference(capacitor)

1. Sep 8, 2009

### stpmmaths

1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

1) "One plate is maintained at +75 V while the other at -75 V by a d.c. supply" means? Does it means that this capacitor is connected to a 150 V d.c. supply or just a 75 V?
2) Why is 75-(-75)? Why don't we just use 75V?
3) Charge stored on each plate is it the same as charge stored in the whole capacitor?

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2. Sep 8, 2009

### kuruman

All that matters with capacitors is the potential difference across the plates because that is the voltage V as in Q = C V. So you can view this as one plate being at potential 0 V and the other at 150 V or -75 V and 75 V, or 250 V and 100 V.
See above. What is the difference in electrostatic potential between the plates?
One plate has positive charge (+Q) and the other plate has negative charge of the same magnitude (-Q). By convention, when we say "the charge on the capacitor", we mean the charge on the positive plate, +Q.

3. Sep 9, 2009

Thanks.