Resistors
• A resistor is any component in the circuit that resists or slows down the flow of current. A light bulb is an example of a resistor.
• A resistor can be used in a circuit to control the current. The higher the resistance is in a circuit, the smaller the current that can flow.
• Some of the energy in electric current is transferred to the resistor as the current flows through it. The transferred electrical energy is changed to useful light or heat energy in appliances such as light bulbs, heaters, stoves and hot water geysers.
New word
resistor – a part of a circuit that slows down the flow of current
Figure 1 Resistors in these appliances heat up to give off useful output energy.
The photograph and notes below explain how the energy transfer and changes take place in an incandescent light bulb.
The conducting wire is connected to the filament.
The filament is a resistor, made of metal (usually tungsten). When electric current flows through the filament, the flow of current is slowed down. Some of the electrical energy is changed to heat energy and then to light energy as the filament gets very hot.
Light bulbs have two metal contact points at the base, which connect to the ends of an electrical circuit. The screw thread contact point is joined to connecting wires inside the bulb. The electrical foot contact is connected to a conducting wire or bulb holder.
The two contact points are separated by an insulator so that electric current cannot flow directly between them instead of through the bulb.
Figure 2 How a light bulb works Unit 2 Components of a circuit 109
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