Free · Physics models
Point Charge Electrostatic Force
Relate signed point charges and separation to electrostatic force in a uniform dielectric.
- Formula & worked example
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Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
Private by default
Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.
Formula and method
Force (F = k==e== (q==1== q==2== / r^^2^^)) = 0.00017975104. The worked example lists its inputs and unit conventions.
F = kq₁q₂/(εr r²); k = 1/(4π ε₀).
Worked example
Enter these known values and leave the other values blank.
- Relative permittivity
- 1
- Charge 1 (q==1==)
- 1 nC
- Charge 2 (q==2==)
- 2 nC
- Distance (r)
- 10 mm
- Force (F = k==e== (q==1== q==2== / r^^2^^))
- 0.000179751 N
- Vacuum permittivity
- 8.854 × 10⁻¹² F / m
Assumptions and limitations
- Point charges, static fields and a uniform linear medium are assumed. Positive signed force denotes repulsion and negative denotes attraction; the scalar is not a vector direction. The retained k default is 8.987551787368176×10⁹ SI, a historical rounded reference.
- Clear the quantity to solve an inverse; keep known quantities fixed with locks. Some inverses are singular or ambiguous and require further known values.
- Unit selectors convert the same physical quantity. Rounded reference constants and presets limit physical accuracy even when arithmetic displays more digits.
Common questions
What does this model assume?
Point charges, static fields and a uniform linear medium are assumed. Positive signed force denotes repulsion and negative denotes attraction; the scalar is not a vector direction. The retained k default is 8.987551787368176×10⁹ SI, a historical rounded reference.
Can I solve for an input?
Editable calculated fields support the captured inverse relationships. Clear the unknown and supply enough independent known values; an inverse must remain within the declared physical domain.
References
Enforce the reviewed model domain: Relative permittivity must be positive. Coulomb constant must be positive. Vacuum permittivity must be positive.