Exam words
identify – find, name and mention something
suggest – give ideas, solutions or reasons for something
Activity 2 Read about fuses Individual work
Read about fuses on the previous page and answer these questions: 1 Identify the purpose of a fuse. 2 Explain why a fuse is made of very thin wire. 3 Suggest why an electrical fault must first be fixed before a burnt-out fuse is replaced.
Short circuits
Figure 3 Exposed wires can lead to a short circuit. Never use damaged electrical cords.
A short circuit occurs when the current flows through a path of lowest resistance, bypassing the rest of the circuit. Because of the low resistance, too much current may flow. This makes the conducting wires very hot, which can cause a fire. A short circuit can occur when connecting wires touch each other directly. This means that the conductor is connected directly to both terminals of a cell or battery and does not pass through a resistor. The short circuit offers an easier route for the current because the connecting wire has much less resistance than the bulb. Most of the current travels along the short circuit and not through the light bulb. The light bulb does not light up and the connecting nichrome wire gets very hot.
Magnetic effect of electric current
Figure 4 This electromagnet is made of an insulated wire wrapped around an iron core.
Electric current can cause metal to become magnetic. We call this the magnetic effect of current. The moving electric current produces a magnetic field around the conductor. The conductor then becomes a temporary electromagnet. An electromagnet is a piece of metal containing iron. It becomes magnetic when an electric current passes around it through a piece of insulated wire. It is a temporary magnet and can be switched on and off.
Uses of electromagnets
Being able to turn a magnet on and off can be very useful. Electromagnets are useful in scrap metal yards for sorting and lifting pieces of metal. They can be used medically to extract iron splinters from people’s eyes. Electromagnets are also used in computer hard drives, electric bells, motors, dynamos, loudspeakers and electromagnetic door locks.
New word
Figure 5 Electromagnets sort and lift metals in scrap yards.
electromagnet – a metal containing iron that becomes magnetic when an electric current passes around it
114 Topic 2 Energy transfer in electrical systems
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