Electricity: Circuits and their Components

Class 07 Science

Electricity is generated in multiple ways - by windmills, by using wind energy, by solar panels capturing the Sun’s energy, by falling water and by using natural gas or coal. The electric supply from these sources reaches homes and factories via wires.

Electric Cell

All electric cells have two terminals; one is called positive (+ ve) while the other is negative (– ve). The metal cap is the positive terminal of the electric cell and the metal disc is the negative terminal. The electric cell is a portable source of electrical energy.

Battery

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.

For many devices, we may need more than one cell. So, we connect two or more cells together. Connecting more than one cell provides energy to the circuit for a longer time and/or more energy.

Electric Lamp

Incandescent Lamp

The filament is attached to two thicker wires that support it. One thick wire connects to the metal case at the lamp’s base, while the other connects to the metal tip at the centre of the base. These form the two terminals of the lamp, and are fixed in a way that they do not touch each other. In such incandescent lamps, the filament gets hot and glows to produce light.

LED Lamp

Many torches in use today have a Light Emitting Diode (LED) lamp, instead of an incandescent lamp. Unlike incandescent lamps, LEDs do not have filaments. They also have two terminals, but one is positive (attached to a longer wire) and the other is negative (the shorter wire). A torch may use one or more LEDs, sometimes of different shapes, in its lamp.

Electrical Circuit

The lamp glows when one terminal of the lamp is connected to one terminal of the electric cell and the other terminal of the lamp to the other terminal of the cell. This setup forms an electrical circuit, which provides a complete path for electric current to flow through the lamp. The lamp glows only when current passes through the circuit.

The direction of electric current in an electrical circuit is taken to be from the positive to the negative terminal of the electric cell. When the terminals of the lamp are connected with those of the electric cell by wires, the current passes through the filament of the incandescent lamp and makes it glow. With an incandescent lamp, it does not matter which of its terminals connects to the positive or negative terminal of the cell. The lamp will glow as long as the circuit is complete and current flows through the filament.

The current can pass through the LED in one direction only. The current passes through the LED only when the positive terminal (longer wire) of the LED is connected to the positive terminal of the battery, and negative terminal (shorter wire) of the LED is connected to the negative terminal of the battery. When current passes through the LED, it glows.

Electric Switch

A switch is a simple device that either completes or breaks a circuit. The switches used for lights and other devices at home work the same way, though they are designed differently.

When the switch is ON, the circuit is closed and current flows from the cell’s positive to negative terminal making the lamp glow. When the switch is OFF, the circuit prevents current flow, and the lamp does not glow. In this OFF position, we say that the circuit is open.

Circuit Diagrams

By using symbols to represent electrical components, it is easier to draw and understand electrical circuits. A representation of an electrical circuit using symbols is called its circuit diagram.

In the symbol for an electric cell, the long line represents the positive terminal, while the short line represents the negative terminal.

In the symbol for an LED, the triangle points to the direction in which the current can flow. The two arrows indicate that light is emitted by an LED.

Electrical Conductors and Insulators

Electric current can pass easily through some materials but not through others. The materials through which electric current can flow easily are called conductors of electricity. The materials through which current cannot pass through are called insulators of electricity.

Silver, copper, and gold are the best electrical conductors. However, for making electrical wires, mainly copper is used due to its comparatively lower cost and abundant supply.

Conductors and insulators are both important. Electrical wires, switches, connectors of plugs, and sockets are made of conductors. Insulators like rubber, plastics, and ceramics are used to cover wires, plug tops, and switches to protect people from electric shocks.