AC is described by peak values, frequency, and sine equations

Alternating Currents — AQA A-Level Physics

Peak voltageThe energyThe capacity to do work. Measured in joules (J). transferred per unit chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). between two points. Measured in volts (V). Informal term for potential difference. V₀ is the maximum voltageThe energyThe capacity to do work. Measured in joules (J). transferred per unit chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). between two points. Measured in volts (V). Informal term for potential difference. reached during the cycle. The voltageThe energyThe capacity to do work. Measured in joules (J). transferred per unit chargeA property of matter that causes it to experience a force in an electromagnetic field. Measured in coulombs (C). between two points. Measured in volts (V). Informal term for potential difference. swings between +V₀ and -V₀.
Peak currentThe rate of flow of charge. Measured in amperes (A). I₀ is the maximum currentThe rate of flow of charge. Measured in amperes (A). reached during the cycle. Same idea: the currentThe rate of flow of charge. Measured in amperes (A). swings between +I₀ and -I₀.
FrequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz). f is the number of complete cycles per second. Unit: hertz (Hz). UK mains: $f = 50 Hz$.
PeriodThe time taken for one complete oscillation or wave cycle. Measured in seconds (s). T is the time for one complete cycle. T = 1/f. For 50 Hz mains, $T = 0.02 s = 20 ms$.
The angular frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz). ω connects frequencyThe number of complete oscillations passing a point per unit time. Measured in hertz (Hz). to the sine function. It tells you how fast the phase angle advances.

\omega = 2\pi f

$\omega$: angular frequency (rad s⁻¹)
$f$: frequency (Hz)

The instantaneous voltage at time t is given by:

V = V_0 \sin(\omega t)

$V$: instantaneous voltage (V)
$V_0$: peak voltage (V)
$\omega$: angular frequency (rad s⁻¹)
$t$: time (s)

Similarly for current:

I = I_0 \sin(\omega t)

$I$: instantaneous current (A)
$I_0$: peak current (A)
$\omega$: angular frequency (rad s⁻¹)
$t$: time (s)

These equations assume the voltage (or current) is zero at $t = 0. If$ the waveform starts at a different point, a phase constant would be added, but AQA doesn't require this.
At t = 0: V = 0. At t = T/4: V = V₀ (first peak). At t = T/2: V = 0 again. At t = 3T/4: V = -V₀ (negative peak). At t = T: $V = 0 (one full cycle complete)$.

Examiner Tips and Tricks

Make sure your calculator is in radians when using $V = V_{0} \sin(\omega t)$.
The argument ωt is in radians.
If you use degrees, you'll get the wrong answer every time.