GCE A/L Physics flashcards

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

SI unit of force

The newton (N), defined as the force that gives a 1 kg mass an acceleration of 1 m s⁻²; in base units it is kg m s⁻².

Systematic error

A constant offset affecting every reading in the same direction, caused by faulty calibration or zero error; it shifts the mean but is not reduced by repetition.

Fractional uncertainty in a power

For y = aⁿ, the fractional uncertainty in y equals n times the fractional uncertainty in a; percentage uncertainty is this multiplied by 100.

Newton's second law

The resultant force on a body equals the rate of change of its momentum; for constant mass this reduces to F = ma.

Principle of moments

A rigid body is in rotational equilibrium when the sum of clockwise moments about any point equals the sum of anticlockwise moments about that point.

Elastic collision

A collision in which both momentum and kinetic energy are conserved; no energy is transferred to internal energy or deformation.

Young modulus

The ratio of tensile stress to tensile strain in the linear region of a stress–strain graph; a measure of a material's stiffness, in pascals.

Limit of proportionality

The point on a force–extension graph beyond which extension is no longer directly proportional to the applied force, so Hooke's law fails.

Elastic potential energy

Energy stored in a deformed elastic object, equal to the area under its force–extension graph; for a spring obeying Hooke's law it is ½kx².

Diffraction grating equation

d sin θ = nλ, where d is the slit spacing, θ the angle of the nth maximum and λ the wavelength; it allows accurate wavelength measurement.

Stationary wave node

A point of permanently zero displacement where destructive superposition occurs; adjacent nodes are separated by half a wavelength.

Coherent sources

Two wave sources with a constant phase difference and the same frequency, required for a stable observable interference pattern.

Kirchhoff's second law

Around any closed loop in a circuit, the sum of electromotive forces equals the sum of potential differences; it expresses conservation of energy.

Capacitor time constant

The product RC, equal to the time for a discharging capacitor to fall to 1/e (about 37%) of its initial charge or potential difference.

Internal resistance

The resistance within a source that causes its terminal potential difference to fall below its emf as current is drawn, V = E − Ir.

Faraday's law of induction

The induced emf in a circuit equals the negative rate of change of magnetic flux linkage through it; the minus sign expresses Lenz's law.

Magnetic flux density

The force per unit current per unit length on a conductor placed perpendicular to a magnetic field, measured in tesla (N A⁻¹ m⁻¹).

Gravitational field strength

The gravitational force per unit mass at a point, equal to GM/r² outside a spherical mass and directed toward its centre.

Ideal gas equation

pV = nRT, relating pressure, volume, amount and absolute temperature; R is the molar gas constant, 8.31 J mol⁻¹ K⁻¹.

First law of thermodynamics

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

Half-life

The time for half the nuclei in a radioactive sample to decay, related to the decay constant by t½ = ln 2/λ.

Binding energy per nucleon

The energy required to remove one nucleon from a nucleus, equal to total binding energy divided by mass number; peaks near iron-56.

Quark composition of proton

Two up quarks and one down quark (uud), giving charge +2/3 + 2/3 − 1/3 = +1 in units of the elementary charge.

Work function

The minimum energy needed to remove an electron from a metal surface; the threshold frequency for photoemission is the work function divided by h.

de Broglie wavelength

The wavelength associated with a moving particle, equal to Planck's constant divided by its momentum, λ = h/mv.

Stopping potential

The reverse potential difference that just prevents the most energetic photoelectrons from reaching the anode, giving maximum kinetic energy as eV.

Simple harmonic motion condition

The acceleration of the body is directly proportional to its displacement from equilibrium and always directed toward that equilibrium position.

Kepler's third law

For planets or satellites, the square of the orbital period is proportional to the cube of the orbital radius: T² = (4π²/GM)r³.

Wien's displacement law

The peak wavelength of black-body radiation is inversely proportional to absolute temperature, λ_max T = 2.90 × 10⁻³ m K.

Hubble's law

The recession speed of a distant galaxy is proportional to its distance from us, v = H₀d, evidence for an expanding universe.

Half-value thickness

The thickness of an absorber that reduces the intensity of a radiation beam to half its incident value; equal to ln 2 divided by the attenuation coefficient.

Doppler ultrasound

A technique using the frequency shift of ultrasound reflected from moving blood to determine flow speed, using the relation Δf/f = 2v cos θ/c.