# Why isn't electric potential zero when the electric field strength is zero?

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Thread starter 7 years ago
#1
The mark scheme answer is C.

E = Q/4piEor2.
V = Q/4piEor.

E = V/r.
So when E = 0, isn't V also 0?

And that contradicts the mark scheme answer of C.

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7 years ago
#2
In those equations what is V is the potential gradient/difference and not the electric potential.

The electric potential is a scalar quantity. Even if in an area the electric potential is non-zero but constant there won't be an electric field generated - so in this area the electric field strength is zero but the electric potential is not zero.

Electric field strength is the negative of the rate of change of electrical potential with distance or the potential gradient. There can be a electrical potential in a region but if there is no change in the electric potential in any direction then there won't be an electric field.

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7 years ago
#3
(Original post by Sayonara)
The mark scheme answer is C.

E = Q/4piEor2.
V = Q/4piEor.

E = V/r.
So when E = 0, isn't V also 0?

And that contradicts the mark scheme answer of C.

You're right that when the electric field (E) is 0, that the potential difference (V) is also 0.

But V is the potential difference, not the potential.

However we never really care what the true potential is, because it is only the potential difference between two points in space that has any physical significance. So if you know what the potential is at all points in space and you add 1000 to each of these numbers, the physics won't' change because the potential difference between any two points will still be the same, even though the true potential has increased by 1000.

So in summary, the potential is never really knowable, and so you cannot say it is 0, or 1000 or whatever, you can only know the potential difference between two points.
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