HSC Physics flashcards

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

Projectile horizontal velocity

In ideal projectile motion air resistance is ignored, so the horizontal velocity component stays constant throughout the flight while only the vertical component changes under gravity.

Centripetal acceleration

The acceleration of an object in uniform circular motion, magnitude v squared divided by radius r, directed toward the centre of the circle because velocity direction changes continuously.

Kepler's third law

For orbits around a central mass, the cube of the orbital radius divided by the square of the period equals GM divided by four pi squared.

Work–energy theorem

The net work done on an object by all forces equals the change in its kinetic energy, allowing speeds to be found from force and displacement data.

Conservation of momentum

If no net external force acts on a system, total momentum before an interaction equals total momentum after; momentum is a vector so components are conserved separately.

Elastic collision

A collision in which both momentum and total kinetic energy are conserved; objects bounce apart with no energy converted to heat, sound or deformation.

Inclined plane components

On a frictionless slope at angle theta, weight resolves into mg sin theta along the slope and mg cos theta perpendicular to it, the latter balanced by the normal force.

Ohm's law

For a conductor at constant temperature, current is directly proportional to potential difference, giving V equals IR where resistance is measured in ohms.

Parallel resistance rule

For resistors in parallel, the reciprocal of total resistance equals the sum of reciprocals of individual resistances, so total resistance is less than the smallest branch resistance.

Magnetic force on wire

A current-carrying wire of length l in a magnetic field B experiences force BIl sin theta, where theta is the angle between the wire and the field direction.

Faraday's law of induction

An emf is induced in a circuit equal to the negative rate of change of magnetic flux through it, multiplied by the number of turns.

Lenz's law

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

Wave equation

Wave speed equals frequency multiplied by wavelength; frequency is fixed by the source and wavelength changes when a wave enters a medium of different speed.

Doppler effect

The observed frequency of a wave shifts higher when source and observer approach and lower when they recede, depending on relative motion through the medium.

Standing wave nodes

Points of zero displacement in a standing wave, spaced half a wavelength apart; antinodes of maximum amplitude lie midway between adjacent nodes.

Speed of light postulate

All inertial observers measure the same vacuum speed of light regardless of their motion or the source's motion, which forces time and length to be relative.

Time dilation

A clock moving relative to an observer runs slow by the Lorentz factor; proper time is measured in the frame where the two events occur at the same place.

Length contraction

An object's measured length along its direction of motion is shorter than its proper length by the Lorentz factor; no contraction occurs perpendicular to motion.

Mass–energy equivalence

Mass and energy are interchangeable via E equals mc squared; a small mass defect releases large energy, explaining nuclear binding and radioactive decay energies.

Photoelectric effect

Light of sufficient frequency ejects electrons from a metal surface; maximum electron kinetic energy equals photon energy minus the work function, independent of intensity.

Work function

The minimum energy needed to remove an electron from a metal surface; it sets the threshold frequency below which no photoelectric emission occurs.

de Broglie wavelength

Every particle has an associated wavelength equal to Planck's constant divided by its momentum, observable for electrons but negligible for everyday objects.

Quantised energy levels

Electrons in atoms occupy discrete energy states; photons are emitted or absorbed with energy equal to the difference between two levels, producing line spectra.

Wien's displacement law

The peak wavelength of blackbody radiation is inversely proportional to absolute temperature, with the product of peak wavelength and temperature constant at about 2.9 millikelvin metres.

Stefan–Boltzmann law

The total power radiated per unit area of a blackbody is proportional to the fourth power of its absolute temperature, with the constant sigma about 5.67 times ten to the minus eight.

Half-life

The time for half the nuclei in a radioactive sample to decay; after n half-lives the remaining fraction is one half raised to the power n.

Binding energy

The energy equivalent of the mass defect of a nucleus, representing the energy needed to separate all its nucleons; higher binding energy per nucleon means greater stability.

Strong nuclear force

The short-range attractive force between nucleons that overcomes proton–proton electrostatic repulsion within the nucleus; it acts over distances of roughly a femtometre.

Standard Model particles

Matter is built from quarks and leptons; forces are carried by gauge bosons such as photons, gluons and W and Z bosons, with the Higgs boson giving mass.

Semiconductor doping

Adding pentavalent atoms creates n-type material with extra electrons; trivalent atoms create p-type material with holes, increasing conductivity at room temperature.

Velocity–time graph area

The area between a velocity–time graph and the time axis equals displacement; area below the axis counts as negative displacement in the opposite direction.

Impulse

The product of force and the time it acts, equal to the change in momentum; a longer contact time reduces the peak force for the same momentum change.

Terminal velocity

The constant speed reached when the upward drag force on a falling object equals its weight, so net force and acceleration become zero.