# Homework Help: Electric field vs. Electric potential

1. Jun 19, 2004

### wave41

Hello everyone...I need help to start on a problem which states that V(r) =V(o) r^2/2R^2...I neeed to find E(r) when R and V(o) are constants...so from defention E= dV/Dr??? This is the part I am not sure how to move on..I have to integrate the equation they gave me keeping the V(o) and R as constants?
Thank you...

2. Jun 19, 2004

$$E = \frac{d}{dr}V(r)$$

V(r) is given, so you get

$$E = \frac{d}{dr}\left(V_0 \frac{r^2}{2R^2} \right)$$

So what's the problem?

3. Jun 19, 2004

### wave41

The problem is that I have a very bad math backround...I am asking if I have to integrate that? Keeping V(o) and R outside the integral...I have not done integrals yet so I am having trouble with it...I have missed math (meaning didn't study it ) from basically 4th grade to 9th so to catch up on it takes me a while...

4. Jun 19, 2004

E is defined as the derivative of V. You have V. You'd then have to differentiate V to get E.

There are no integrals involved.

Now, if you had E and you were asked to find V, then you'd have to integrate. But it's the other way around, hence differentiate.

The problem is asking you to evaluate the derivative I described above.