Fields

Gravitational field strength formula

g = GM/r²

Electric field strength (radial)

E = kQ/r²

Electric field strength (uniform)

E = V/d

Magnetic force on wire

F = BIL sinθ

Magnetic force on moving charge

F = BQv sinθ

Direction of gravitational force

Always attractive

Direction of electric force

Attractive or repulsive (depends on charge)

Direction of magnetic force

Perpendicular to field & velocity (uses left-hand rule)

Source of gravitational field

Mass

Source of electric field

Charge

Source of magnetic field

Moving charge or current

Gravitational potential formula

V = –GM/r

Electric potential formula

V = kQ/r

Type of gravitational field around a point mass

Radial field

Type of electric field between plates

Uniform field

What does magnetic flux equal?

Φ = BA cosθ

Unit of gravitational field strength

N kg⁻¹

Unit of electric field strength

N C⁻¹ or V m⁻¹

Unit of magnetic flux density

Tesla (T)

Field lines around a point charge

Radial: away from +, toward –

Field lines around a wire

Circular around the wire

Field lines between magnets

Straight from North to South

Work done in electric field

W = QΔV

Work done in gravitational field

W = mΔV

Particle motion in uniform magnetic field

Circular path (if velocity ⟂ field)

Law governing gravitational fields

Newton’s Law of Gravitation

Law governing electric fields

Coulomb’s Law

Law governing magnetic induction

Faraday’s Law and Lenz’s Law

Magnetic force is maximum when…

θ = 90° (perpendicular to field)