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# Uniform electric field / Electric field watch

1. Electric field strength, E = (Electric force on a small charge, F)/(charge of object, Q)

Am I right in saying that the above equation can only be used for non-uniform fields?

And the below equation should be used for uniform fields?

E = V/d

Thanks
2. In short, they're both the same thing. If you substitute in the formula for V, you'll find they're the same.

The initial formula, which can be written like this:

is the formula for Electric Field Strength. It can also be written like this:

It depends on what information you're given, as to which one you use.
3. E=F/Q is always valid - for non-uniform and uniform fields. It is the definition of electric field - force exerted on unit positive charge. The only difference is that in a uniform field it will be the same everywhere, as the force on a unit positive charge will be the same everywhere, whilst in a non-uniform field it will vary in space, as the force on unit positive charge will depend upon the location of that unit positive charge.

E=V/d is the electric field at any point between two parallel plates, where V is the potential difference between the plates and d is the separation of the plates. It is only valid for the uniform field between two parallel plates.
4. (Original post by Qwertish)
In short, they're both the same thing. If you substitute in the formula for V, you'll find they're the same.

The initial formula, which can be written like this:

is the formula for Electric Field Strength. It can also be written like this:

It depends on what information you're given, as to which one you use.
SO

Electric field strength, E = (Electric force on a small charge, F)/(charge of object, Q)

refers to uniform fields as well?
5. (Original post by GPODT)
SO

Electric field strength, E = (Electric force on a small charge, F)/(charge of object, Q)

refers to uniform fields as well?
It is the definition of the electric field and works in every case, so yes.
6. (Original post by GPODT)
SO

Electric field strength, E = (Electric force on a small charge, F)/(charge of object, Q)

refers to uniform fields as well?
Yes. That is the most generic definition, and works in all cases.
E=F/Q is always valid - for non-uniform and uniform fields. It is the definition of electric field - force exerted on unit positive charge. The only difference is that in a uniform field it will be the same everywhere, as the force on a unit positive charge will be the same everywhere, whilst in a non-uniform field it will vary in space, as the force on unit positive charge will depend upon the location of that unit positive charge.

E=V/d is the electric field at any point between two parallel plates, where V is the potential difference between the plates and d is the separation of the plates. It is only valid for the uniform field between two parallel plates.
(Original post by 3nTr0pY)
It is the definition of the electric field and works in every case, so yes.
(Original post by Qwertish)
Yes. That is the most generic definition, and works in all cases.
Thank you all!

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