UEE Physics flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Newton's second law

The net force on a body equals the rate of change of its momentum, ΣF = dp/dt, which reduces to ΣF = ma when mass is constant.

Work-energy theorem

The net work done on a particle equals its change in kinetic energy. For conservative forces only, mechanical energy is conserved.

Centripetal acceleration

For uniform circular motion the acceleration has magnitude v²/r = ω²r and points toward the centre; it changes direction, not speed.

Kepler's third law

For circular orbits the period squared is proportional to the orbital radius cubed: T² = 4π²r³/(GM), where M is the central mass.

Conservation of angular momentum

When the net external torque on a system is zero, its angular momentum L = Iω remains constant, so reducing I increases ω.

Ideal gas law

Relates pressure, volume and temperature: pV = nRT = NkT, with R ≈ 8.31 J mol⁻¹ K⁻¹ and k ≈ 1.38×10⁻²³ J K⁻¹.

First law of thermodynamics

The change in internal energy equals heat added to the system minus work done by the system: ΔU = Q − W.

Root-mean-square speed

The typical molecular speed in a gas, v_rms = √(3kT/m) = √(3RT/M), increasing with the square root of absolute temperature.

Carnot efficiency

The maximum possible efficiency of a heat engine operating between hot and cold reservoirs is η = 1 − T_C/T_H, using absolute temperatures.

Entropy change

For a reversible process the entropy change is ΔS = Q_rev/T; the entropy of an isolated system never decreases.

Simple harmonic motion

Motion where acceleration is proportional and opposite to displacement, a = −ω²x, giving sinusoidal displacement with period T = 2π/ω.

Resonance

A large amplitude response occurs when a periodic driving frequency matches a system's natural frequency; damping lowers and broadens the peak.

Standing wave condition

A string fixed at both ends supports wavelengths λ_n = 2L/n, so the fundamental frequency is v/(2L) and harmonics are integer multiples.

Doppler effect

The observed frequency shifts when source and observer move relative to each other: approaching raises frequency, receding lowers it.

Sound intensity level

A logarithmic measure of sound intensity: β = 10 log₁₀(I/I₀) decibels, with reference intensity I₀ = 10⁻¹² W m⁻².

Gauss's law

The electric flux through a closed surface equals the enclosed charge divided by ε₀; it simplifies fields with high symmetry.

Capacitor energy

The energy stored in a charged capacitor is U = ½CV² = ½QV = Q²/(2C), stored in the electric field between the plates.

Faraday's law

A changing magnetic flux through a circuit induces an EMF equal to the negative rate of change of flux: EMF = −dΦ/dt.

Lenz's law

The direction of an induced current is such that it opposes the change in magnetic flux that produced it, consistent with energy conservation.

Kirchhoff's loop rule

Around any closed loop in a circuit, the algebraic sum of potential differences is zero, expressing energy conservation per unit charge.

Total internal reflection

Light travelling from a denser to a less dense medium is completely reflected when the incidence angle exceeds θ_c = arcsin(n₂/n₁).

Thin lens equation

Relates object distance u, image distance v and focal length f: 1/f = 1/u + 1/v, with transverse magnification m = −v/u.

Double-slit fringe spacing

For Young's experiment the spacing between adjacent bright fringes on a distant screen is Δy = λD/d, where D is slit-screen distance.

Rayleigh criterion

Two point sources are just resolved when their angular separation equals 1.22λ/D for a circular aperture of diameter D.

Malus's law

The intensity transmitted through a polariser is I = I₀ cos²θ, where θ is the angle between the incident polarisation and the polariser axis.

Photoelectric equation

The maximum kinetic energy of emitted electrons is hf − φ, where φ is the work function; below threshold frequency no emission occurs.

de Broglie wavelength

Every particle has an associated wavelength λ = h/p, observable for electrons and other particles with small momentum.

Bohr energy levels

Hydrogen levels are E_n = −13.6 eV/n²; a photon is emitted when an electron drops to a lower level, with energy equal to the difference.

Radioactive half-life

The time for half the nuclei in a sample to decay, related to the decay constant by t½ = ln2/λ; decay is exponential.

Uncertainty propagation

For independent random uncertainties, combine partial contributions in quadrature: δz = √(Σ(∂z/∂x_i)²δx_i²).

Systematic versus random error

Systematic errors shift readings consistently and are not reduced by averaging; random errors scatter and are reduced by repeated measurements.

Linearising a graph

Rearranging a relationship into y = mx + c form lets the gradient and intercept be found from a best-fit straight line.