How to use it
- Choose to solve for force, distance or the size of charge 1.
- Enter the other values with their units. For charges, use one shared unit.
- Read the result. For a force, the tool also says whether it is attractive or repulsive.
How it works
F = k|q₁q₂|/r². The distance is r = √(k|q₁q₂|/F) and charge 1 is |q₁| = F·r²/(k·|q₂|). When solving for a charge or distance, signs are not needed because only the magnitude is determined.
Worked example
Two charges of +1 µC at 10 cm: F = 8.9875517923e9 × (1e-6)² ÷ 0.1² = 0.8988 N, repulsive. If one is −1 µC the force has the same size but is attractive.
Tips
- Convert the distance carefully: 10 cm is 0.1 m, and an error there is squared in the result.
- The force on each charge has the same size, by Newton’s third law.