Calculators
Electric Field Calculator
Calculate electric field from a point charge and distance.
Calculate the ideal electric field produced by a single point charge at a specified distance in vacuum.
Electric field magnitude
898755.18 N/C
Radial direction
away from the positive charge
N/C and V/m are dimensionally equivalent electric-field units. The direction shown is for the field created by the source charge.
About This Tool
An electric field describes the force that a positive test charge would experience per unit charge at a location. For an isolated point charge in vacuum, its magnitude depends on the source charge and the inverse square of the distance. This calculator applies E = k|q|/r², reports the radial direction implied by the charge sign, converts common units, and performs all calculations locally in your browser.
How To Use It
- Enter the source charge. Use a positive value for a positive charge or a negative value for a negative charge.
- Choose the charge unit and enter a distance greater than zero from the point charge.
- Select the electric-field result unit. N/C and V/m represent the same electric-field dimension.
- Interpret the direction as radial: away from a positive point charge and toward a negative point charge.
Examples
1 µC at 0.1 m
A +1 µC point charge at 0.1 m produces an ideal field magnitude of about 8.99 × 10^5 N/C, directed away from the positive charge.
Negative source charge
Changing the source charge from positive to negative leaves the magnitude unchanged for the same |q| and distance, but reverses the radial direction toward the charge.
Inverse-square behavior
Doubling the distance from the same point charge reduces the field magnitude to one quarter because E is proportional to 1/r².
Useful Notes
Point-charge electric field formula
For a point charge in vacuum, E = k|q|/r², where E is electric-field magnitude, q is source charge, r is distance from the charge, and k is Coulomb's constant, approximately 8.9875517923 × 10^9 N·m²/C².
Direction and charge sign
Electric-field direction is defined as the direction a positive test charge would accelerate. The field points radially away from a positive source charge and radially toward a negative source charge. A zero source charge produces zero field, so there is no meaningful radial field direction.
N/C and V/m
Newtons per coulomb and volts per metre are equivalent SI expressions for electric-field strength. This calculator offers both forms plus kilo-scaled versions for convenient reading.
Why distance matters so much
The inverse-square relationship means field strength falls rapidly with distance. If distance is multiplied by three, the ideal field becomes one ninth as large; if distance is halved, the field becomes four times as large.
Model assumptions and limitations
The formula models a single ideal point charge in vacuum. Extended charge distributions, multiple charges, conductors, dielectric materials, boundaries, and time-varying electromagnetic effects require additional methods. At r = 0 the ideal point-charge expression is singular, so the calculator requires a positive distance.
FAQ
What is the formula for electric field from a point charge?
The magnitude is E = k|q|/r² for an isolated point charge in vacuum. The sign of q determines the radial direction rather than making the magnitude negative.
Why does the calculator use absolute charge for magnitude?
Magnitude is non-negative. A negative source charge changes the field direction toward the charge, while a positive source charge makes the field point away.
Are N/C and V/m the same?
Yes. For electric field, 1 N/C is equivalent to 1 V/m.
Can I calculate the net field from several charges?
Not with this single-point-charge calculator. Electric fields from multiple sources must be added as vectors, including their directions and geometry.
Related Tools
Coulomb's Law Calculator
Calculate electrostatic force between two point charges.
Force Calculator
Solve force, mass, or acceleration with F = ma.
Scientific Calculator
Scientific math functions with degree and radian modes.
Length Converter
PopularConvert common length and distance units.