Electric interaction
What is an electric field?
An electric field describes the electric force that a positive test charge would experience at a particular location.
Electric field strength is a vector quantity. This calculator determines its magnitude using either force and test charge or a point source charge and distance.
Force and charge model
Electric field from force
Electric field strengthE = F ÷ q
- E is electric field strength in newtons per coulomb.
- F is electric force in newtons.
- q is test-charge magnitude in coulombs.
Point-charge model
Electric field from a point charge
Point-charge electric fieldE = kQ ÷ r²
- Q is the source charge magnitude in coulombs.
- r is distance from the source charge in metres.
- kis Coulomb's constant.
Rearranged equations
Solve for force, charge, or distance
Electric force
F = Eq
Test charge
q = F ÷ E
Source charge
Q = Er² ÷ k
Distance
r = √(kQ ÷ E)
Worked example
Calculate field from force and charge
- Electric force is 0.02 N.
- Test charge is 4 × 10⁻⁶ C.
- Apply E = F ÷ q.
- Substitute the values: E = 0.02 ÷ 4 × 10⁻⁶.
- Electric field strength is 5000 N/C.
Field direction
Positive and negative source charges
The electric field points away from a positive source charge and toward a negative source charge.
The calculator accepts positive magnitudes and reports field magnitude. Determine direction from the source-charge sign and geometry.
Unit guidance
Electric field units and conversions
- Electric field: newtons per coulomb (N/C).
- Electric force: newtons (N).
- Electric charge: coulombs (C).
- Distance: metres (m).
- 1 microcoulomb = 1 × 10⁻⁶ C.
Model limitations
Assumptions and limitations
The force-charge model assumes that the test charge is sufficiently small that it does not significantly alter the original electric field.
The point-charge model assumes a stationary point source in vacuum or approximately in air. Extended charge distributions, dielectric materials, multiple charges, shielding, and complex geometry require more advanced field analysis.
Related tools
Continue your electrostatics analysis
Use the Coulomb's Law Calculator to calculate the electric force between two point charges.
Use the Force Calculator to calculate force, mass, or acceleration using Newton's second law.
Questions and answers
Electric field calculator FAQ
What formulas does the electric field calculator use?
It uses E = F/q for force and test-charge calculations, and E = kQ/r² for the field produced by a point source charge.
What is the unit of electric field strength?
Electric field strength is measured in newtons per coulomb, written N/C. It is also equivalent to volts per metre.
How do I calculate electric force from field strength?
Multiply electric field strength by the test charge using F = Eq.
How do I calculate the field around a point charge?
Multiply Coulomb's constant by the source-charge magnitude and divide by the square of the distance using E = kQ/r².
Does this calculator show electric-field direction?
No. It calculates magnitude. The field points away from a positive source charge and toward a negative source charge.