Notes On The Heating Effect of Electric Current - CBSE Class 7 Science
 When an electric current flows through a wire, the wire gets hot. This is known as the heating effect of electric current. The factors that affect the production of heat in a wire through which an electric current flows are the length and thickness of the wire, the duration of flow of current, and the material of the wire. Some  appliances that work on the property of the heating effect of electric current are electric room heater, electric roti maker, electric iron, toaster, hair dryer, electric stove, immersion water heater, food warmer, electric coffee maker, electric rice cooker and geyser. These appliances have coils of wire known as heating elements which produce heat. As current flows through these electrical appliances, the heating elements turn bright orange red in colour. This is because a huge amount of heat is produced. An electric bulb also works on the heating effect of electric current. The filament of an electric bulb gets heated to such a high temperature that it starts glowing. Different appliances have different types of heating elements. The type of heating element depends on the function of the appliance. Some appliances are required to produce more heat than others. Electric Fuse An electric fuse is a safety device used to prevent damage to an electrical circuit when excessive current flows through it.The electric fuse works on the principle of the heating effect of electric current. It consists of a piece of wire made of a metal or an alloy of low melting point. As the current increases beyond a limit, the wire in the electric fuse melts and breaks off. The fuse is then said to have blown off. The circuit is broken and current stops flowing through it. Thus a fuse prevents fires. There are various types of fuses. Some fuses are used only in buildings, while others are used in appliances. Reasons for Excessive Current When all the appliances are connected to the same socket, they draw more current, and so the load increases. When the insulation on the wires is torn, two wires carrying current may touch each other directly. This causes a spark, which leads to fire. This is termed as a short circuit. If a fuse is not used, overloading and short circuits occur which results in fire. Compact Fluorescent Lamp (CFL) We use electric bulbs to obtain light but it also gives heat. This is not desirable. This results in the wastage of energy. CFL’s do not depend on the heating effect of electricity to produce light, since they do not use filaments. Using CFL’s instead of ordinary bulbs minimises wastage of electricity. In CFL’s, light is generated using two electrodes. The fluorescent coating inside each tube makes the light brighter. ISI Mark We should purchase only appliances that bear an ISI mark. ISI stands for Indian Standards Institute. If an appliance bears the ISI mark, it means that it is safe and will not waste electrical energy. Moreover, it is a mark of quality. Miniature Circuit Breakers (MCBs) The problem with the fuses is that whenever overloading occurs the fuse wire melts and it has to be replaced to complete the circuit. This problem is overcome in miniature circuit breakers (MCBs) which are widely used nowadays. MCBs are switches that turn off automatically when there is an overload or a short circuit. After solving the problem in the circuit, the switch can be turned back on, and then the current flows as usual.

#### Summary

 When an electric current flows through a wire, the wire gets hot. This is known as the heating effect of electric current. The factors that affect the production of heat in a wire through which an electric current flows are the length and thickness of the wire, the duration of flow of current, and the material of the wire. Some  appliances that work on the property of the heating effect of electric current are electric room heater, electric roti maker, electric iron, toaster, hair dryer, electric stove, immersion water heater, food warmer, electric coffee maker, electric rice cooker and geyser. These appliances have coils of wire known as heating elements which produce heat. As current flows through these electrical appliances, the heating elements turn bright orange red in colour. This is because a huge amount of heat is produced. An electric bulb also works on the heating effect of electric current. The filament of an electric bulb gets heated to such a high temperature that it starts glowing. Different appliances have different types of heating elements. The type of heating element depends on the function of the appliance. Some appliances are required to produce more heat than others. Electric Fuse An electric fuse is a safety device used to prevent damage to an electrical circuit when excessive current flows through it.The electric fuse works on the principle of the heating effect of electric current. It consists of a piece of wire made of a metal or an alloy of low melting point. As the current increases beyond a limit, the wire in the electric fuse melts and breaks off. The fuse is then said to have blown off. The circuit is broken and current stops flowing through it. Thus a fuse prevents fires. There are various types of fuses. Some fuses are used only in buildings, while others are used in appliances. Reasons for Excessive Current When all the appliances are connected to the same socket, they draw more current, and so the load increases. When the insulation on the wires is torn, two wires carrying current may touch each other directly. This causes a spark, which leads to fire. This is termed as a short circuit. If a fuse is not used, overloading and short circuits occur which results in fire. Compact Fluorescent Lamp (CFL) We use electric bulbs to obtain light but it also gives heat. This is not desirable. This results in the wastage of energy. CFL’s do not depend on the heating effect of electricity to produce light, since they do not use filaments. Using CFL’s instead of ordinary bulbs minimises wastage of electricity. In CFL’s, light is generated using two electrodes. The fluorescent coating inside each tube makes the light brighter. ISI Mark We should purchase only appliances that bear an ISI mark. ISI stands for Indian Standards Institute. If an appliance bears the ISI mark, it means that it is safe and will not waste electrical energy. Moreover, it is a mark of quality. Miniature Circuit Breakers (MCBs) The problem with the fuses is that whenever overloading occurs the fuse wire melts and it has to be replaced to complete the circuit. This problem is overcome in miniature circuit breakers (MCBs) which are widely used nowadays. MCBs are switches that turn off automatically when there is an overload or a short circuit. After solving the problem in the circuit, the switch can be turned back on, and then the current flows as usual.

#### Activities

Activity 1 w3.ualg.pt/~jlongras/aulas has deveoped an interactive online simulation in which one can understand the heating effects of electricity and Joule's law. Go to Activity Activity 2 tutorvista.com has deveoped an interactive online simulation in which one can understand the heating effects of electricity and Joule's experiment to determine the mechanical equivalent of heat i.e., Joule's constant. Go to Activity Activity 3 www.harcourtschool.com has deveoped an interactive online simulation in which one can understand the heating effects of electricity by a simulation of glowing an electric bulb. Go to Activity

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