SACE Physics exam 2026Exam: Thu 5 Nov · SACE Board timetable

$t_0$ is the proper time - the time interval measured in the frame where the two events happen at the same place (the moving clock's own frame). $t$ is the longer (dilated) time measured by the observer who sees the clock moving.

Both point toward the centre of the circle. The centripetal force is the net inward force; it is not a new kind of force but the role played by tension, gravity, friction or a normal force.

The momentum of an object is the product of its mass and velocity:

It is a vector pointing in the direction of motion, measured in $\text{kg m s}^{-1}$ (equivalently N s).

Elastic collision: total kinetic energy is conserved as well as momentum. The objects bounce apart with no loss of $E_k$.

For an ideal (100% efficient) transformer, power in equals power out, so also:

$N_p$, $N_s$ are the numbers of turns on the primary and secondary; $V$ and $I$ are voltages and currents.

The direction of an induced current is always such that its own magnetic field opposes the change in flux that created it. An induced current resists the change, whether the flux is increasing or decreasing.

Standard hand rules give the force direction for a positive charge. For a negative charge (such as an electron), the force is in the opposite direction. Always check the sign of the charge before quoting a direction.

$\varepsilon$ is the induced EMF (V), $N$ the number of turns in the coil, and $\dfrac{\Delta\Phi}{\Delta t}$ the rate of change of magnetic flux ($\text{Wb s}^{-1}$). The minus sign is Lenz's law (next dot point), giving the direction of the induced EMF.

An emission spectrum is a set of bright coloured lines on a dark background, produced when excited atoms drop to lower levels and emit photons.

$E_{k,\text{max}}$ is the maximum kinetic energy of an ejected electron, $hf$ the photon energy, and $W$ the work function (the minimum energy needed to free an electron from the metal). Emission occurs only when $hf \ge W$, i.e. above the threshold frequency $f_0 = W/h$.

The photon carries the electromagnetic force.

Constructive interference (maximum): the waves arrive in phase. The path difference is a whole number of wavelengths, $n\lambda$ ($n = 0, 1, 2, \dots$).