A charge creates an electric field around it that pushes on other charges. The field points away from positive charges and towards negative ones, weakening with the square of the distance.
How to use the Electric Field of a Point Charge Calculator
- Charge q
- Distance r
- Relative permittivity ε_r
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter the charge, the distance and the relative permittivity of the medium.
Tips
- Keep track of signs of charges – like charges repel, unlike attract.
- Use SI units (C, V, A, T) in the formulas; the menus convert prefixes.
- Vacuum permittivity ε₀ = 8.854 × 10⁻¹² F/m and permeability μ₀ = 4π × 10⁻⁷ H/m.
- For AC power, include the power factor.
Common mistakes to avoid
- Using microcoulombs as coulombs.
- Forgetting the √3 factor in three-phase power.
- Mixing RMS and peak values.
Inputs explained
| Field | What to enter |
|---|---|
| Charge q | Units: nC, µC, C, pC, e |
| Distance r | Units: cm, mm, m, in, ft |
| Relative permittivity ε_r | A number |
Example values
How the main result changes when Charge q changes and everything else stays at the example values above:
| Charge q (nC) | Electric field E (V/m) |
|---|---|
| 2.5 | 2,246.8879 |
| 3.75 | 3,370.3319 |
| 5 | 4,493.7759 |
| 6.25 | 5,617.2199 |
| 7.5 | 6,740.6638 |
| 10 | 8,987.5518 |
Formula
E = k·|q| / (ε_r·r²)Worked example
Inputs — Charge q: 5 nC; Distance r: 10 cm; Relative permittivity ε_r: 1.
Results — Electric field E = 4,493.775896 V/m; Direction = Away from the charge.
Key terms
- Electric field
- Force per unit positive test charge.
Frequently asked questions
What are the units of electric field?
V/m, equivalent to N/C.
What is the field 1 m from 1 C?
About 9 × 10⁹ V/m – an enormous charge.
How does the field change in water?
It is reduced 80-fold (ε_r ≈ 80).
What field breaks down air?
About 3 MV/m.
What formula does the Electric Field of a Point Charge Calculator use?
E = k·|q| / (ε_r·r²).