Case 1
- First charge q₁
- 0.000001C
- Second charge q₂
- 0.000001C
- Distance r between them
- 0.1m
0.898755N
Open with these valuesCoulomb's Law Calculator
0.898755N
Result: 0.898755 NThe force between two point charges is kₑ times the product of the charges, divided by the square of the distance. Two microcoulombs 10 cm apart pull or push with about 0.9 N. Enter charges in coulombs — a microcoulomb is 0.000001 — and the distance in metres.
Worked examples
Case 2
- First charge q₁
- 0.000002C
- Second charge q₂
- 0.000003C
- Distance r between them
- 0.5m
0.215701N
Open with these valuesCase 3
- First charge q₁
- 1C
- Second charge q₂
- 1C
- Distance r between them
- 1m
8,987,551,790.000000N
Open with these valuesHow it's calculated
F = kₑ × |q₁ × q₂| ÷ r²
- StepEnter both charges in coulombs — 1 µC is 0.000001.
- StepA negative sign is allowed; only the magnitude of the force is shown.
- ResultEnter the separation in metres and read the force in newtons.
Reference table
| q₁, q₂, r | What it is | Force |
|---|---|---|
| 0.000005, 0.000005, 2 | Two 5 µC charges, two metres apart | 0.056172 |
| 0.000002, 0.000003, 0.5 | 2 µC and 3 µC, half a metre apart | 0.215701 |
| 0.000001, 0.000001, 0.1 | Two 1 µC charges, repelling | 0.898755 |
| 0.000001, -0.000001, 0.1 | The same pair, now attracting | 0.898755 |
| 1, 1, 1 | One coulomb each, one metre — the constant itself | 8987551790 |
Questions
How do I calculate the force from Coulomb's law?
Multiply the Coulomb constant by the product of the two charges, then divide by the square of the distance. Coulombs and metres give the force in newtons — two 1 µC charges 0.1 m apart give about 0.899 N.
What is Coulomb's law?
It describes the electrostatic force between two stationary point charges. The force grows with the product of the charges and falls with the square of the distance; like charges repel and opposite charges attract, both with the same magnitude.
What value does this use for the Coulomb constant?
kₑ = 8.98755179 × 10⁹ N·m²/C², the CODATA figure 8.9875517862 × 10⁹ rounded to nine significant digits. Textbooks often shorten it further to 9 × 10⁹, which is about 0.14 per cent high.
Why does doubling the distance quarter the force?
Because the distance is squared in the denominator. The force scales with 1 ÷ r², so twice the separation means a quarter of the force and three times the separation a ninth of it.
What units should I use?
Coulombs for each charge and metres for the distance, which gives newtons. Convert small charges first: 1 microcoulomb is 0.000001 C and 1 nanocoulomb is 0.000000001 C.
Sources and last check
Information, not professional advice.