Class 7 Science

# Electric Current

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.

#### Review Questions:

Question 1: What is the SI unit of electric current?

Question 2: What is an electric cell?

Answer: It is device which produces electric charge because of some chemical reaction.

## 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 constantan which is a metal with very high melting point.