LC Physics cheat sheet

Equations of uniform acceleration: v = u + at, s = ut + ½at², v² = u² + 2as; use when acceleration is constant in a straight line.

Newton's second law: F_net = ma; the acceleration is in the same direction as the resultant force and inversely proportional to mass.

Momentum p = mv is conserved in a closed system; impulse FΔt equals the change in momentum Δp.

Weight W = mg, where g ≈ 9.8 m/s² near Earth's surface; mass is a scalar measured in kg and weight is a force in N.

Work W = Fd cosθ and power P = W/t; kinetic energy Ek = ½mv² and gravitational potential energy Ep = mgh.

For circular motion at constant speed: centripetal acceleration a = v²/r and centripetal force F = mv²/r directed toward the centre.

A body is in equilibrium when the net force and net moment are zero; moment = force × perpendicular distance from the pivot.

Hooke's law: the extension of a spring is directly proportional to the applied force up to the limit of proportionality, F = kx.

Projectile motion: horizontal and vertical motions are independent; horizontal velocity is constant if air resistance is ignored, vertical acceleration is g downward.

Wave equation: v = fλ; period T = 1/f; frequency is the number of oscillations per second, measured in hertz (Hz).

Transverse waves vibrate perpendicular to energy transfer; longitudinal waves vibrate parallel; sound in air is longitudinal.

Refraction obeys Snell's law: n₁ sin θ₁ = n₂ sin θ₂; refractive index n = c/v, where c is the speed of light in vacuum.

For total internal reflection, the angle of incidence must exceed the critical angle C, where sin C = 1/n (from denser to less dense medium).

Diffraction is the spreading of waves at an obstacle or gap; noticeable when the gap width is comparable to the wavelength.

Two coherent sources have a constant phase difference; constructive interference occurs when path difference is a whole number of wavelengths.

Sound frequency range for normal human hearing is about 20 Hz to 20 kHz; speed of sound in air at room temperature is about 340 m/s.

Thin lens equation: 1/f = 1/u + 1/v with real-is-positive sign convention; magnification m = v/u.

The electromagnetic spectrum from longest to shortest wavelength: radio, microwave, infrared, visible, ultraviolet, X-ray, gamma ray.

Coulomb's law: F = kQ₁Q₂/r², with k ≈ 8.99 × 10⁹ N·m²/C²; force is repulsive for like charges and attractive for opposite charges.

Electric field strength E = F/q; field lines point away from positive charge and toward negative charge.

Ohm's law V = IR for a conductor at constant temperature; resistance R = ρL/A depends on resistivity, length and cross-sectional area.

Resistors in series: R_total = R₁ + R₂ + ...; in parallel: 1/R_total = 1/R₁ + 1/R₂ + ...

Electrical power P = VI = I²R = V²/R; energy transferred E = Pt, with electrical energy often measured in kWh.

Capacitance C = Q/V; energy stored in a capacitor E = ½CV²; parallel-plate capacitor C = εA/d.

Magnetic force on a current-carrying conductor: F = BIL sinθ; on a moving charge: F = qvB sinθ.

Faraday's law: induced emf ε = −dΦ/dt; Lenz's law states the induced current opposes the change producing it.

For sinusoidal AC, V_rms = V_peak/√2 and I_rms = I_peak/√2; transformer voltage ratio V_p/V_s = N_p/N_s for an ideal transformer.

Photon energy E = hf = hc/λ, where h ≈ 6.63 × 10⁻³⁴ J·s; photon energy is proportional to frequency.

Photoelectric effect: electrons are emitted from a metal surface when incident light exceeds the threshold frequency; maximum kinetic energy depends on frequency, not intensity.

Einstein's photoelectric equation: hf = φ + E_k(max), where φ is the work function of the metal.

de Broglie wavelength: λ = h/p = h/(mv); particles have wave-like behaviour observable at small scales.

Bohr model: electrons occupy discrete energy levels; a transition between levels emits or absorbs a photon of energy ΔE = hf.

Atomic number Z is the number of protons; mass number A is protons plus neutrons; isotopes have the same Z but different A.

Radioactive decay is random and spontaneous; half-life T½ is the time for half the nuclei in a sample to decay.

Decay law: N = N₀e^(−λt), with activity A = λN; λ = ln2/T½.

In nuclear reactions, charge and mass number are conserved; mass defect appears as released energy via E = mc².

Temperature in kelvin: T(K) = T(°C) + 273.15; absolute zero is 0 K, the lowest possible temperature.

Heat energy changing temperature: Q = mcΔT, where c is specific heat capacity in J/(kg·K).

Heat energy changing state: Q = mL, where L is specific latent heat; temperature stays constant during a phase change.

Ideal gas law: PV = nRT, with R ≈ 8.31 J/(mol·K); for a fixed mass of gas, PV/T = constant.

Boyle's law: at constant temperature, PV = constant; Charles's law: at constant pressure, V/T = constant.

Conduction transfers heat through solids by particle collisions; convection transfers heat through fluid movement; radiation transfers heat by electromagnetic waves.

Thermal equilibrium occurs when two objects in contact have the same temperature and no net heat flows between them.

Specific heat capacity is the energy needed to raise 1 kg of a substance by 1 K; specific latent heat is energy needed to change 1 kg between phases at constant temperature.

A thermometer is calibrated using fixed points such as the ice point (0 °C) and steam point (100 °C) at standard pressure.