Electric Field Strength Calculator
Calculate electric field strength from a point charge or between parallel plates using Coulomb law.
Electric Field Strength
The electric field describes the force that a charged object exerts on other charges in its vicinity. It is a fundamental concept in electrostatics and electrical engineering.
Point Charge Formula (Coulomb’s Law):
E = k × |Q| / r²
Where:
- E = electric field strength (N/C or V/m)
- k = Coulomb’s constant (8.9875 × 10⁹ N·m²/C²)
- Q = charge in coulombs (C)
- r = distance from the charge in meters (m)
Parallel Plates Formula:
E = V / d
Where:
- V = voltage (potential difference) between the plates in volts (V)
- d = distance between the plates in meters (m)
What each variable means:
- Electric field (E) — measured in newtons per coulomb (N/C) or volts per meter (V/m). These units are equivalent.
- Charge (Q) — the source charge creating the field, in coulombs. 1 coulomb is a very large charge; typical values are in microcoulombs (μC) or nanocoulombs (nC).
- Distance (r) — how far from the charge you are measuring the field.
- Voltage (V) — the electric potential difference driving the field between plates.
Field strength reference values:
| Source | Electric Field Strength |
|---|---|
| Fair weather atmosphere | ~100 V/m |
| Under a thundercloud | 10,000–30,000 V/m |
| Air breakdown (spark) | ~3,000,000 V/m |
| Inside a capacitor (typical) | 10,000–100,000 V/m |
| Near a Van de Graaff generator | ~1,000,000 V/m |
When to use this calculator:
- Physics and engineering coursework
- Designing capacitors and electrical components
- Understanding electrostatic safety distances
- Calculating forces on charged particles
Practical example: A 1 μC (1 × 10⁻⁶ C) charge creates an electric field of about 9,000 N/C at a distance of 1 meter. At 10 cm, that field increases to 900,000 N/C — showing how rapidly the field strengthens as you get closer.
Tips:
- The electric field from a point charge follows an inverse-square law — doubling the distance reduces the field by 4×.
- Between parallel plates, the field is uniform (constant strength everywhere between the plates).
- Electric field lines point away from positive charges and toward negative charges.