Electric Field Strength 2

Physics: AQA A Level, topic 7.3.3

A Uniform Electric Field

A uniform field is one which has the same strength at every point in the field.

Uniform field

A uniform field has the same strength everywhere, it can be made from parallel charged plates.
If two charged plates are held a distance apart the field between them will be uniform
The field lines will travel straight from the positive plate into the negative plate.

Calculating the field

If two plates are held apart with different charges they will have a voltage difference between them. The equation for the field strength is:
Field strength = voltage drop ÷ distance between the plates
$E=V/d$

Work done in an Electric Field

Two oppositely charged parallel plates provide a uniform electric field. Uniform fields have field lines that are equally spaced, straight and parallel.

Moving between charged plates

The work done in moving a positively charged particle from the negative plate to the positive plate is:
$W= F \times d$
Where F is a constant force acting on the charged particle and d is the separation of the plates.

Derivation

The work done in moving a positively charges particle is also, by definition:
$W = Q \times \Delta V$
These two expressions are equal to each other:
$F\times d=Q\times \Delta V$

Derivation 2

Rearranging this gives:
$\frac{F}{Q}=\frac{\Delta V}{d}$
Because $\frac{F}{Q}$ $\frac{F}{Q}$ is defined as electric field strength, electric field strength between two parallel plates is:
- $E = \frac{\Delta V}{d}$

Test yourself on Electric Field Strength 2

What is the equation for the field strength of a uniform field?
In what direction do the field lines point in a uniform field?

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