SACE Stage 2 Physics flashcards

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

Average velocity

Displacement divided by the time interval taken. It is a vector, so its sign indicates direction of motion, unlike average speed which uses total distance.

Uniform acceleration equations

For constant acceleration: v = u + at, s = ut + ½at² and v² = u² + 2as. They cannot be applied when acceleration changes during the motion.

Projectile motion components

Horizontal and vertical motions are independent. Horizontal velocity stays constant while vertical acceleration equals g downward, so time of flight follows from vertical motion alone.

Centripetal acceleration

For circular motion, a = v²/r directed toward the circle's centre. Speed may be constant while velocity changes continuously because direction changes.

Conservation of momentum

In an isolated system, total momentum before an interaction equals total momentum after. This holds for elastic and inelastic collisions and for explosions.

Lorentz factor

γ = 1/√(1 − v²/c²), always at least 1. It grows without limit as speed approaches c, quantifying relativistic time, length and mass effects.

Proper time

The time interval measured by an observer at rest relative to the event, between two events at the same place. It is the shortest measured interval.

Rest energy

E₀ = mc², the energy equivalent of an object's mass when it is at rest. Total relativistic energy is γmc², so kinetic energy is (γ − 1)mc².

Coulomb's law

The electrostatic force between point charges is F = kq₁q₂/r², acting along the line joining them. It is repulsive for like charges and attractive for unlike charges.

Electric field strength

Force per unit positive charge, E = F/q, measured in N/C or V/m. For a point charge the field is kq/r², directed away from positive charge.

Parallel plate field

Between oppositely charged parallel plates the field is approximately uniform with E = V/d. A charge q moved through potential difference V gains energy qV.

Resistance and resistivity

R = ρL/A shows resistance rises with length and falls with cross-sectional area. Resistivity ρ is a property of the material, not the sample's shape.

Series and parallel resistance

Series resistances add directly and share the same current. For parallel resistors the reciprocals add, and each branch experiences the same potential difference.

Electrical power

Power dissipated in a component is P = VI = I²R = V²/R. Energy used follows from E = Pt, often expressed in kilowatt-hours.

Magnetic force on a wire

A current-carrying wire in a magnetic field experiences force F = BIL sin θ, where θ is the angle between the current and the field direction.

Faraday's law

The induced emf equals the negative rate of change of magnetic flux linkage, ε = −N ΔΦ/Δt. The minus sign expresses Lenz's law opposing the change.

Magnetic flux

Φ = BA cos θ, the product of field strength and area perpendicular to the field, measured in webers. Flux linkage multiplies flux by the number of turns.

Wave equation

For any wave, speed equals frequency multiplied by wavelength: v = fλ. Frequency is fixed by the source, so wavelength adjusts when speed changes.

Superposition principle

When waves overlap, their displacements add algebraically. Constructive interference gives a larger amplitude; destructive interference gives a smaller amplitude or zero.

Double slit fringe spacing

Bright fringes in Young's experiment are spaced by Δy = λL/d, where L is the slit-to-screen distance and d is the separation between the slits.

Diffraction grating equation

Principal maxima occur where d sin θ = nλ, with n the order number. Smaller slit spacing d produces wider angular separation between successive orders.

Snell's law

n₁ sin θ₁ = n₂ sin θ₂ describes refraction at a boundary, where n = c/v. Light entering a slower, denser medium bends toward the normal.

Total internal reflection

Occurs when light travels from a denser to a less dense medium at angles beyond the critical angle, given by sin θc = n₂/n₁. No light refracts out.

Standing wave nodes

In a standing wave, nodes are points of zero displacement and antinodes are points of maximum amplitude. Adjacent nodes are separated by half a wavelength.

Photon energy

A photon carries energy E = hf = hc/λ, where h is Planck's constant. Higher frequency or shorter wavelength means a more energetic photon.

Photoelectric effect

Light ejects electrons from a metal only if photon energy exceeds the work function. Maximum kinetic energy of emitted electrons equals hf minus the work function.

Atomic energy levels

Electrons in atoms occupy discrete energy levels. A photon is emitted with energy equal to the difference between levels when an electron drops.

de Broglie wavelength

λ = h/(mv) relates a particle's momentum to its matter wavelength. Larger mass or speed gives a shorter wavelength and less noticeable wave behaviour.

Alpha decay

A nucleus emits a helium nucleus of two protons and two neutrons. The mass number falls by four and the atomic number falls by two.

Beta-minus decay

A neutron converts into a proton, emitting an electron and an antineutrino. The atomic number rises by one while the mass number stays unchanged.

Half-life

The time for half the nuclei in a sample to decay. After n half-lives, the fraction remaining is (½)ⁿ, and activity falls by the same fraction.

Mass defect and binding energy

The mass of a nucleus is less than the mass of its separate nucleons. This defect converts to binding energy by E = Δmc²; larger binding energy per nucleon means greater stability.