Class seven electric current and its effects
Answers
Electric Current: The flow of electric charge is called electric current. In an electric circuit, the charge is often carried by moving electrons. The SI unit of electric current is Ampere (A). The SI unit of electric charge is Coulomb.
Electric Circuit: The path through which electric charge moves is called electric circuit.
Symbols in Electric Circuit: Different components of electric circuit are shown by certain symbols. Use of symbol makes it easy to represent an electric circuit. Use of standard symbol makes it easy to understand for anybody. For example; a TV mechanic can identify different components of a TV by looking at its circuit diagram.
Electric Cell: It is a device which produces electric charge because of some chemical reactions. The cell which is used in a torch is called dry cell. The wet cells are used in car batteries. A normal dry cell gives an output of 1.5 Volt (V).
Battery: A group of cells is called battery. More than one cell is used in most of the devices; because the device needs more than 1.5 V of power.
Closed Circuit: When the circuit is complete, it is called closed circuit. Current flows only in a closed circuit.
Open Circuit: When the circuit is incomplete, it is called open circuit. Current does not flow in an open circuit.
Heating Effect of Electric Current
When electric current flows through a conducting wire, the temperature of wire increases. This is called heating effect of electric current.
Devices Which Work on Heating Effect of Electric Current: Incandescent bulb is an example of a device which works because of the heating effect of electric current. The filament of bulb is made of tungsten. Tungsten has very high melting point and that is the reason it is used in electric bulb. Moreover, argon gas is filled inside the bulb. Argon prevents the filament from catching fire. Electric iron, water heater, geyser, toaster, etc. are some other devices which work on heating effect of electric current.
Elements of Heating Appliances: A heating appliance has a highly coiled wire or a metallic rod. This is called the element of the heating appliance. The highly coiled structure increases the surface area and thus provides more heat. The elements are usually made of constantant which is a metal with very high melting point.
Electric Fuse: Electric fuse is a safety device which is used in household wirings and in many appliances. Electric fuse has body made of ceramic and two points for attaching the fuse wire. The fuse wire melts whenever there is overload in the wiring. This breaks the circuit and helps in preventing damage to costly appliances and to the wiring. In electrical devices a glass fuse is often used. This is a small glass tube, in which lies the fuse wire.
MCBs (Miniature Circuit Breaker): MCBs have been replacing electric fuse from wirings at most of the places. The electric fuse has a big practical problem. Whenever the wire fuses, one needs to replace the wire to resume electric supply. More often than not, this proves to be a cumbersome task. Miniature circuit breakers break the circuit automatically. One just needs to switch it on to resume the electric supply. Many models of MCBs have a built in mechanism by which the electric supply is automatically resumed
Magnetic Effect of Electric Current:Hans Christian Oersted (1777 – 1851) was the first to show that electric current also produces magnetic effect. He kept a magnetic compass near a current carrying conductor. It was observed that the magnetic compass shows deflection, when the current passes through the conductor.
Electromagnet: Magnetic effect of electric current has been used in making powerful electromagnets. For this, wire is wrapped around an iron rod in many turns and electric current is supplied to the wire. As long as the current is supplied the iron rod behaves like a magnet. More number of turns makes more powerful magnet. Electromagnet is used in electric bells and also in powerful cranes.
Electric Bell: Electric Bell is composed of two rods of cast iron. Coil is made around the iron rods. A metallic strip is placed parallel to the coils. The metallic strip is fitted with a hammer at one end. Another end of the strip is connected to the circuit. A gong is placed in a position so that it can be hit by the hammer. When current flows in the circuit, the cast iron rods become electromagnet and attract the metallic strip. The metallic hammer hits the gong because of that. Once the metallic strip is pulled towards the electromagnet, it gets disconnected from the point and there is a break in the circuit. A spring pulls the metallic strip back because no magnetism is left in the electromagnet. This cycle continues and the electric bell produces a ringing sound.