Paper 2 Alternating Current Answers

Q1 Sinusoidal Voltage

1. $24\mathrm{V}$. [1]
2. $\omega =200\pi =2\pi f$, so $f=100\mathrm{Hz}$. [2]
3. $V_{rms}=V_0/\sqrt{2}=24/\sqrt{2}=17.0\mathrm{V}$. [2]

Q2 AC Power in a Resistor

1. $I_{rms}=V_{rms}/R=12.0/18=0.667\mathrm{A}$. [2]
2. $P=V_{rms}{I}_{rms}=12.0(0.667)=8.0\mathrm{W}$. [2]
3. Rms values give the equivalent dc value producing the same mean heating effect in a resistor. [2]

Q3 Rectification

1. Alternating input reverses polarity/direction; rectified output remains one polarity/direction. [2]
2. Its magnitude still varies with time, so it is pulsating dc unless smoothed. [2]
3. It charges when the output is high and discharges through the load when output falls, reducing ripple. [1]