Electric field strength

The formula for electric field strength is:

$$E = \frac{F}{q}$$

Where:

• $E$ is the electric field strength (measured in Newtons per Coulomb, N/C).
• $F$ is the electric force experienced by the test charge (measured in Newtons, N).
• $q$ is the magnitude of the test charge (measured in Coulombs, C).

For a point charge $Q$ creating the field, the electric field strength at a distance $r$ from the charge is given by:

$$E = \frac{k|Q|}{r^2}$$

Where:

• $k$ is Coulomb's constant ($8.99 \times 10^9 \text{ N}\cdot\text{m}^2/\text{C}^2$).
• $|Q|$ is the magnitude of the source charge (C).
• $r$ is the distance from the source charge to the point of interest (m).

The direction of the electric field strength is the direction of the force that a positive test charge would experience. This means it points away from positive source charges and towards negative source charges.