Chapter 14 - Electric Current and its Effects Notes
1. Electric cell has 2 terminals -• Positive terminals
• Negative terminals
2. Electric component Symbols
3. The positive terminal of one cell is connected to the negative terminal of the next cell. Such a combination of two or more cells is called a battery.
4. In the bulb there is a thin wire, called the filament, which glows when an electric current passes through it. When the bulb gets fused, its filament is broken.
5. When an electric current flows through a wire, the wire gets heated. It is the heating effect of current.
6. The coil of wire is called an element.
7. The amount of heat produced in a wire depends on its material, length and thickness.
8. An electric circuit is an arrangement of different components such as the electric cell, battery, switch, electric bulb and wire. It is the complete path from one terminal of the electric cell through the bulb and back to the other terminal of the electric cell.
9. Wires made from special materials melt quickly and break when large electric currents are passed through them. These wires are used for making electric fuses.
10. When electric current passes through a wire, it behaves, like a magnet. This is the magnetic effect of the electric current. In fact, electric current can be used to make magnets.
11. An electromagnet is an example of the magnetic effect of the electric current. It is used in many devices like electric bell, loudspeakers, telephone, etc.
12. An electric bell mainly consists of an electromagnet, a hammer and a gong.
13. An electric bulb is used for light but it also gives heat. This is not desirable. This results in the wastage of electricity. This wastage can be reduced by using fluorescent tube lights in place of the bulbs. Compact fluorescent lamps (CFLs) also reduce wastage and can be fixed in the ordinary bulb holders. However, before buying bulbs or tubes, or CFLs, look for the ISI mark of the Bureau of Indian Standards. In fact, before buying any electrical appliance, look for this mark. The ISI mark ensures that the appliance is safe and wastage of energy is minimum.
14. One reason for excessive currents in electrical circuits is the direct touching of wires. This may happen if the insulation on the wires has come off due to wear and tear. This may cause a short circuit. Another reason for excessive current can be the connection of many devices to a single socket. This may cause overload in the circuit.
15. These days Miniature circuit breakers (MCBs) are increasingly being used in place of fuses. These are switches which automatically turn off when current in a circuit exceeds the safe limit.
16. Hans Christian Oersted was the first person who noticed the deflection of compass needle every time the current was passed through the wire. So, when electric current passes through a wire, it behaves like a magnet. This is the magnetic effect of the electric current. In fact, an electric current can be used to make magnets.
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