AC Fundamentals Check

1. Ohm's law states:

V = I / RV = P × RP = V / IV = I × R

2. Why do buildings use AC instead of DC?

AC wiring is cheaper to install and needs no earthingAC delivers the same power while drawing much less currentDC distribution is illegal in commercial buildings under the UK wiring regulationsTransformers make AC efficient to distribute, and motors run well on it

3. Power factor is the ratio of:

Real power to apparent powerPeak demand to average demandVoltage to currentEnergy used to energy billed

4. A poor power factor (say, 0.7) means:

The supply voltage has sagged below its statutory minimumThe building is actually drawing less energy than its billing meters are recordingExtra current flows for the same useful power, incurring chargesThe site's equipment is running unusually efficiently

Knowledge check