Coulomb's Law Calculator - Electric Force, Charge & Distance
Use this Coulomb's law calculator to solve electrostatic force, charge magnitude, or distance with unit-aware results.
Coulomb's Law Calculator
Results
Coulomb's law works best for point charges or small charged objects separated by a consistent medium.
What is a Coulomb's Law Calculator?
A Coulomb's law calculator finds the electrostatic force between two charges or rearranges the formula to solve for charge or distance. It is useful when you know some values from a physics problem and need the missing value without losing track of units.
The calculator handles signed charges, common charge units, distance units, and medium effects. That means you can enter classroom values such as microcoulombs and centimeters, then get force in newtons or another practical unit. For circuit work, pair it with the electrical resistance calculator.
How Coulomb's Law Works
The Coulomb's law formula calculator uses F = k x |q1 x q2| / r^2 in vacuum or air. Here, k is the Coulomb constant, q1 and q2 are charges in coulombs, and r is the distance in meters between charge centers.
Distance has a squared effect. If the charges stay the same and distance doubles, the force becomes one quarter as large. If the charges are inside a material, relative permittivity divides the force, so water or glass can reduce the interaction compared with air.
Understanding Your Results
The primary result is the value you selected in the Solve For menu. The panel also shows force magnitude, both charges, distance, the medium factor, and the exact rearranged formula used. If you need to combine multiple force directions, use the net force calculator.
Attraction and repulsion come from charge signs. Same-sign charges repel, while opposite-sign charges attract. When solving for an unknown charge magnitude, the calculator reports magnitude because a separate sign convention is needed to assign direction.
How to Use the Coulomb's Law Calculator
- Choose whether you want to solve electric force, charge 1, charge 2, or distance.
- Enter the known charges with signs and choose C, mC, uC, nC, or pC.
- Enter the known distance or force, then select the matching input units.
- Choose the medium preset or enter a custom relative permittivity.
- Review the solved value, interaction type, and formula line in the results panel.
Where Coulomb's Law is Useful
This electric force calculator is most helpful for electrostatics homework, lab preparation, charged particle examples, and quick checks of inverse-square behavior. It can also help you compare how changing charge, distance, or medium changes force, while the force converter helps translate newtons into other units.
Because the calculator accepts microcoulombs and nanocoulombs, you can work in the units often used in textbook problems. The SI conversion happens internally so the formula remains consistent. For related electronics ratios, try the voltage divider calculator.
Important Assumptions and Limits
Coulomb's law is a point-charge model. It works best when each charged object is small compared with the distance between them. Large charged surfaces, uneven charge distributions, and changing fields need more advanced methods.
The calculator also assumes static charges in a consistent medium. If charges are moving quickly, the medium changes, or nearby objects strongly distort the electric field, treat the result as a first approximation.
Frequently Asked Questions (FAQ)
Q: What is Coulomb's law?
A: Coulomb's law describes the electric force between two charged objects. The force grows with the product of the charges and gets weaker with the square of the distance between their centers.
Q: What is the Coulomb's law formula?
A: The common formula is F = k x |q1 x q2| / r^2. This calculator also lets you divide by relative permittivity when the charges are in a material instead of vacuum or air.
Q: How do you calculate electric force between two charges?
A: Convert both charges to coulombs and distance to meters, multiply the charge magnitudes, multiply by Coulomb's constant, then divide by distance squared. Use the charge signs to decide attraction or repulsion.
Q: Can Coulomb's law calculate attraction and repulsion?
A: Yes. The force magnitude uses the absolute value of q1 x q2. If the charges have the same sign, they repel. If the signs are opposite, they attract.
Q: What units does this Coulomb's law calculator support?
A: The calculator supports C, mC, uC, nC, and pC for charge; meters, centimeters, millimeters, inches, and feet for distance; and N, mN, uN, kN, and lbf for force.
Q: When is Coulomb's law most accurate?
A: Coulomb's law is most accurate for point charges or small charged objects whose separation distance is large compared with their size. It also assumes static charges and a consistent surrounding medium.