21.6 Uses of capacitors

• Domestic electricity is supplied as alternating current; the direction of the current changes rapidly and repeatedly as the supply voltage cycles from positive to negative.
• A rectifier circuit can be used to change an alternating voltage to a smooth direct circuit.
• A diode is used in the rectifier circuit to allow current to flow in only on direction, the capacitor smooths the voltage and becomes almost direct voltage of constant value.
• The ripple in the voltage can be kept small by making the time constant of the circuit much greater than the period of the alternating voltage.