1. Jun 7, 2010

### ojsimon

Hi

I am sure this is very basic but i am struggling to derive or work this out, and i have looked, on the internet and text books and can't find this.

The electric potential at a point is defined as the work done per unit charge to move a small test charge from infinity to that point.

And an equation for it is : EP = k*(Q/R)

I want to get back to the definition from this equation, but i cant get very far:

here is what i have done: WD= work done

Q/R = (wd/v)/R
= wd/vR

But i can't go much further without it just going back to the original form.... Can anyone help me?

Thanks

2. Jun 7, 2010

### tiny-tim

hi ojsimon!

(what's v ? )

work done = ∫ force d(distance) = ∫R kQ/r2 dr

(and d(work done)/dr = force)

3. Jun 7, 2010

### ojsimon

sorry v was meant to be voltage and came from the equation v=wd/q

Thanks although i don't quite understand your integral?

Thanks

4. Jun 7, 2010

### tiny-tim

The integral is the force integrated from infinity to the distance R, since the PE is the work done to get the charge from infinity to R.