Electric and magnetic fields

Learning objectives

Describe electric charge, its conservation and its quantisation in units of the elementary charge e = 1.60 × 10⁻¹⁹ C, and explain charging by friction, by contact and by induction

Apply Coulomb's law F = kq₁q₂/r² with k = 1/(4πε₀), and find the resultant force on a charge due to two or more point charges

Define electric field strength as the force per unit positive test charge, calculate E = kq/r² near a point charge and E = V/d between parallel plates, and sketch the field patterns for a point charge, two charges and a parallel-plate arrangement

(HL) Define electric potential as V = kq/r and electric potential energy as Ep = kq₁q₂/r, relate field strength to the potential gradient through E = −ΔV/Δr, and use the electronvolt as a unit of energy

Describe and sketch the magnetic field patterns around a bar magnet, a long straight current-carrying conductor, a flat circular coil and a solenoid, and apply the right-hand grip rule to find the field direction

Compare gravitational and electrostatic fields, noting that both obey an inverse-square law while gravitational forces are only attractive and electrostatic forces may be attractive or repulsive