Physics

1st law (Inertia): An object remains at rest or in uniform motion unless acted upon by a resultant external force. 2nd law: The net force on an object equals the rate of change of momentum: F = ma (constant mass) or F = Δp/Δt. 3rd law: For every action force, there is an equal and opposite reaction force acting on a different object. Forces always come in Newton's 3rd law pairs.

For an object in uniform circular motion: • Speed v is constant but direction changes → acceleration exists • a = v²/r OR a = ω²r Direction: always towards the centre of the circle (centripetal — 'centre-seeking'). Centripetal force (the net force providing this acceleration): F = mv²/r = mω²r This is not a new force — it is the resultant of existing forces (e.g. gravity, tension, friction).

When light of sufficient frequency shines on a metal surface, electrons are emitted (photoelectrons). Key observations that classical wave theory could not explain: • No electrons below threshold frequency regardless of intensity • KE of electrons depends on frequency, not intensity • Emission is instantaneous Einstein's equation: Ek(max) = hf − φ • h = Planck's constant (6.63 × 10⁻³⁴ J s) • f = frequency of incident light • φ = work function (minimum energy to release an electron)

Faraday's law: The magnitude of the induced EMF is proportional to the rate of change of magnetic flux linkage. ε = −dΦ/dt (HL: ε = −NΔΦ/Δt for N turns) Lenz's law: The direction of the induced current is such that it opposes the change in flux that caused it. The minus sign in Faraday's law represents Lenz's law. Together they form the basis for generators, transformers, and induction motors.