Electric Field & Coulomb's Law Calculator
Calculate electric force (Coulomb's law), field strength, and electric potential for point charges. With real-world comparisons.
Electric Fields Guide
Coulomb's Law
F = kq₁q₂/r², where k = 8.99×10⁹ N·m²/C² (Coulomb's constant), q₁ and q₂ are charges in Coulombs, and r is the distance in metres. Like charges (both positive or both negative) repel; opposite charges attract. The force follows an inverse-square law, just like gravity. Example: two charges of 1 μC separated by 10 cm: F = 8.99×10⁹ × 10⁻⁶ × 10⁻⁶ / 0.01 = 0.899 N.
Electric Field Strength
Electric field strength E = F/q = kq/r², measured in N/C or V/m. It is the force per unit positive charge at that point. The field around a positive charge points outward; around a negative charge it points inward. Field lines never cross. The Earth's atmosphere has an electric field of approximately 100–200 V/m near the surface (negative charge on the ground, positive at high altitude). Near a thundercloud, field strengths can reach 20,000 V/m, triggering lightning.
Electric Potential
Electric potential V = kq/r, measured in volts. It is the work done per unit charge to bring a positive charge from infinity to that point. Potential energy of two charges: U = kq₁q₂/r. Electric potential is a scalar (no direction), while electric field is a vector. The relationship: E = −dV/dx (field is the negative gradient of potential). Equipotential surfaces are perpendicular to field lines.
Everyday Applications
Photocopiers (xerography): use electric fields to attract toner particles to charged areas. Inkjet printers: charge droplets and deflect them with electric fields. Electrostatic precipitators: ionise smoke particles so they are attracted to oppositely charged plates — removes 99.9% of particulates from power station flue gas. Defibrillators: use electric current to reset heart rhythm. Capacitors: store electric charge and energy for smoothing power supplies in all electronic devices.
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