Electric Field of a Point Charge Calculator
Electric field strength and potential at a distance from a point charge, and the force on a test charge placed there — Coulomb’s constant, SI units.
How it works
E = k·q ÷ r² · V = k·q ÷ r · F = q_test · E (k = 8.99 × 10⁹ N·m²/C²)
A point charge fills space with a radial field whose strength falls with the square of distance — the same geometry as gravity and light. The potential falls only as 1/r. Field lines leave positive charges and enter negative ones; a positive test charge feels a force along the field, a negative one against it. Fields from several charges add as vectors.
Worked example
5 µC at 20 cm: 8.99 × 10⁹ × 5 × 10⁻⁶ ÷ 0.04 = 1.12 × 10⁶ N/C; a 2 µC test charge feels 2.25 N of repulsion.
Frequently asked questions
What is a typical field strength?
Air breaks down at about 3 × 10⁶ V/m; the field near the Earth’s surface on a clear day is about 100 V/m.
Does this work inside a charged sphere?
Outside a uniformly charged sphere it behaves as a point charge; inside a conducting sphere the field is zero.
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This calculator is for educational purposes. Double-check important results before acting on them.