Electric Fields and Forces

Vocabulary and key concepts from physics lecture notes regarding the definition, calculation, and properties of electric fields.

Electric Field

The force that a unit positive charge would experience if placed at a specific point in space.

Field (General Definition)

A term that signifies how some distributed quantity, which could be a scalar or a vector, varies with position.

Electric Field Formula ($E(r)$)

E(r) = rac{1}{4\pi\varepsilon_0} \frac{Q}{r^2} \hat{r}, where $\hat{r} = \mathbf{r}/r$ is a unit vector from the origin to the point $r$.

Force and Electric Field Relationship

$F(r) = q E(r)$, meaning the force experienced by a charge is equal to the charge multiplied by the electric field at its location.

SI Unit of Electric Field

Newtons per Coulomb ($N/C$).

Source Charge

The charge $Q$ that produces the electric field in the surrounding space.

Test Charge

The charge $q$ that tests the effect of the source charge; it should be negligibly small so as not to disturb the source charge's position.

Electric Field Direction (Positive Point Charge)

The field points radially outwards from the charge.

Electric Field Direction (Negative Point Charge)

The field points radially inwards towards the charge.

Newton's Third Law in Electrostatics

The principle consistent with Coulomb's law stating that the sum of internal forces in a system of charges is zero ($F_1 + F_2 + F_3 = 0$).

$$\hat{r}$$

A unit vector from the origin to the point $r$, defined as $\mathbf{r}/r$.