Resistors often look like tiny painted cans with two wires, one at each end. The two wires are identical and it does not matter which way they are connected in the circuit. Wire wound resistors are used where the resistor has to dissipate a lot of heat. Some resistors are designed to change value when heated. They are called thermistors and are used in temperature measuring circuits.
Some resistors change in value when exposed to light.
They are called light-dependent resistors. Variable resistors are also available. These can usually be operated by means of a knob or a slide on the control panel. Inductors and capacitors 2.3 Simple inductors are made up of tightly wrapped multiple wire loops. Real differences arise when the currents through them vary in time.