Electric field strength
The electric force per unit positive charge at any point in space. For a point charge Q, the electric field strength at distance r is E = kQ/r² = Q/(4πε₀r²) where k = 8.99 × 10⁹ N·m²/C² (or 1/(4πε₀)). Field direction is radial from positive charges, toward negative charges.
Formula
E = kQ/r² = Q/(4πε₀r²)
Real World
The Van de Graaff generator used in school physics demonstrations builds up static charge on a metal dome; the intense radial electric field around it is strong enough to make hair stand on end and produce visible sparks to a grounded conductor.
Exam Focus
State field direction explicitly — away from positive, toward negative — as mark schemes often award this separately from the formula.
How well did you know this?