Electric Field Strength

Key Stage 5

Meaning

Electric field strength is the force per unit charge exerted on a small positive test charge placed at a point in the field.

About Electric Field Strength

• Electric field strength is given by the symbol 𝐸.
• The unit of electric field strength is Newtons per Coulomb (N/C) or volts per metre (V/m).
• The direction of the electric field is the direction of the force that would act on a positive test charge.
• Electric fields can be represented by field lines; the density of these lines indicates the field strength.

Formula

Electric Field Strength is given by the general formula:

• \(𝐸=\frac{𝐹}{𝑄}\)

Where,

𝐹 is the force experienced by a charge 'Q' in the field.

and

𝑄 is the charge in that field.

The Electric field strength around a point charge is given by:

• \(𝐸=𝑘\frac{𝑄}{𝑟^2}\)

Where:

𝑘 is the Coulomb's constant

𝑄 is the point charge causing the field

and

𝑟 is the distance from that point charge

Since;

• \(𝑘=\frac{1}{4\pi\varepsilon_0}\)

Then:

• \(𝐸=\frac{1}{4\pi\varepsilon_0}\frac{𝑄}{𝑟^2}\)

or

• \(𝐸=\frac{𝑄}{4\pi\varepsilon_0𝑟^2}\)

Where:

\[\varepsilon_0\] is the permittivity of free space