Contents
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