An oscilloscope can be used to measure the potential difference across a resistor during the discharge of a capacitor. An oscilloscope has a Y-gain and time-base setting. The Y-gain can be used to measure potential difference and the time-base measures time.Capacitors are used in smoothing circuits to avoid sudden voltage variations and spikes especially during switching on and switching off appliances. These spikes may damage sensitive electronic equipment connected to the mains supply.