Electric Field Formula
Calculate the electric field strength created by a point charge.
Describes the force a charge exerts on its surroundings.
The Formula
E = k × |q| / r²
The electric field describes the force that would be exerted on a positive test charge at any point in space. It points away from positive charges and toward negative charges.
Variables
| Symbol | Meaning |
|---|---|
| E | Electric field strength (N/C or V/m) |
| k | Coulomb's constant (8.99 × 10⁹ N⋅m²/C²) |
| q | Source charge creating the field (Coulombs) |
| r | Distance from the charge (meters) |
Example 1
Find the electric field 0.3 m from a +5 μC charge
E = 8.99 × 10⁹ × 5 × 10⁻⁶ / (0.3)²
E = 44,950 / 0.09
E ≈ 499,444 N/C ≈ 5.0 × 10⁵ N/C
Example 2
What force does a +2 μC charge feel in a field of 1000 N/C?
F = q × E = 2 × 10⁻⁶ × 1000
F = 0.002 N = 2 mN
When to Use It
Use the electric field formula when:
- Mapping the electric field around charged objects
- Calculating the force on a charge placed in an external field
- Designing capacitors and electronic components
- Understanding how electric fields store energy