# Electric Potential and Electric Field Strength

1. Jun 14, 2005

### ylem

Hey!!

I've got my A-Level Physics exam on Thursday, and I'm just doing some past papers and I'm totally confused! Please help!

One of the questions (multiple choice) was saying which statement was incorrect.

The answer was: Electric potential is zero whenever electric field strength is zero.

I don't get how that's wrong....?

(The whole fields part of the syllabus is my worst, which could explain why I'm totally confused! :uhh: )

2. Jun 14, 2005

### Dr.Brain

Electric Field is related to potential as:

$E=- \frac{dV}{dR}$

E can only be zero if V is constant .

So what can be the possible condition as per above such that V is zero when E is zero? Is it possible? ..What are the possible conditions in which V can be zero?

3. Jun 14, 2005

### Chi Meson

Since electric field strength is a vector quantity, the E-field from two positive charges can cancel (if you test a point in space between them).

Potential is not a vector. THink of it more like "pressure." Between the two positive chages there is a potential contributed by both charges to that point in space. Sort of like if two people push on a balloon, one on each side,with equal force. TOtal force will cancel, but the pressure in the balloon builds up. (This analogy falls apart on so many levels, but it is a good start to recognizing how vectors and scalars add up differently).

4. Jun 14, 2005

### ylem

I'm sorry, but I still don't understand....

5. Jun 15, 2005

### saltrock

OMG I think we will be sitting for the same exam>I am also totally confused with the past paper question related to electric potential.If i get my head round it i'll let ya know

6. Jun 20, 2005

### Oerg

All theyre trying to say is that Electric field strength is a vector quantity and electric potential is a scalar quantity. Suppose you have an electric field strength of $0Vm^{-1}$ acting on a test charge by 2 charge particles of 1C and -1C. The electric potential in this case wouldnt be 0, it would be 2V.

Last edited: Jun 20, 2005
7. Jun 23, 2005

### ylem

That kinda makes sense! Wasn't on the exam though (which is good in a way I suppose) not that it matters 'cos I totally messed it up anyway! There was a question about discharge from a capacitor and I was in such a rush to get finished I didn't even use the equation thingy!! Such a fool....!! Gutted.

8. Jun 24, 2005

### Oerg

Oh yeh, in the example i gave, it shouldnt be 2V. You should plug the distance between the two charged particles and the charge into the electric potential equation. Somehow I cant edit my posts anymore.