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Formula Charge in an electric field Electric force    Electric charge    Electric field

Formula
Formula: Charge in an electric field
Force on a positive charge in the E-field of a plate capacitor
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Electric force

Unit
Magnitude of the force experienced by a charge (e.g. electron) in an electric field \( E \).

If you place a charge \( q \) in an electric field \( E \), this charge is accelerated along the field lines by the electric force. A positive charge is accelerated in the direction of the electric field lines and a negative charge is accelerated against the electric field lines.

Electric charge

Unit
Electric charge from a particle, such as an electron or proton.

The charge determines in which direction the electric force points - you can see this by its sign. For positive charges, the sign is a plus - so a force acts on this particle in the direction of the electric field lines. This is the case, for example, with protons, alpha particles, or positively charged ions, such as \( \text{Na}^+ \). For negative charges, the sign is a minus - so a force acts on this particle against the electric field lines. You can observe this for example with electrons.

An electron carries a negative charge \( q ~=~ -1.602 \cdot 10^{-19} \, \text{C} \). A proton, on the other hand, carries a positive charge: \( q ~=~ +1.602 \cdot 10^{-19} \, \text{C} \). Negative charges have a minus before the value of the charge and positive charges have a plus.

Electric field

Unit
Electric field tells how big the electric force is on an electric charge. The field strength is illustrated by field lines. The closer field lines are to each other, the greater is the field strength there, and the greater is the electric force acting on a charge there. The field lines can be straight like in a plate capacitor. Then the force always points in the same direction. But field lines can also be curved; then the force points in different directions, depending on where you place the charge \(q\).

Sconvert the formula according to the electric field strength: \( E ~=~ \frac{F_{ \text{E} }}{q} \), as you can see it is "force per charge".

During a thunderstorm, for example, there is a very large electric field between the earth and clouds; it reaches values above \( 150 \, 000 \, \frac{\text V}{\text m} \).

The electric field generated by a charged particle (e.g. an electron) can be determined by Coulomb's law.