# Homework Help: Electric Energy Potential and Capacitors

1. Oct 2, 2011

### neshepard

1. The problem statement, all variables and given/known dataSo this is from a past test put up as a study guide, but I'm stumped here. The question is:

A spark jumps between two electrodes, transferring a charge of 5 μC in 2 × 10−3 s. The
constant current I that would transfer the same charge in the same time is

3. The attempt at a solution
The solution is 2.5e-3A.

What is the formula to use? Is this to be treated as a capacitor therefore U=1/2QC? Just need a nudge to get my head around it for the test Tuesday.

Thanks

2. Oct 2, 2011

### PeterO

It is not a formula you need, it is contemplation of units.

Current is usually quoted in amperes, which means 1 Coulomb per second.
this spark involved much less that 1 Coulomb, but transferred in much less than a whole second. Think about it.

[Or use I = Q/t if you must]

3. Oct 2, 2011

### neshepard

Thanks. I can never remember the various SI units for things. I end up sticking to Amp, Volt, etc, and this seems to be the down fall of my understanding. But they just don't stick. Anyway, I know the time was fast, and would play a key part, but not where.

Cheers