Electricity is an essential part of our daily life. We use it to light our houses, run fans, cook food, cool or heat rooms and power many appliances. But have you ever wondered what electric current is and what its effects are? In this chapter we study electric current, the symbols used in circuit diagrams, and the various effects of electric current such as heating, magnetic and chemical effects.
A simple electric circuit consists of a cell or battery, connecting wires and a device like a bulb or switch. When the circuit is complete, current flows through it, and when there is a break, the current stops. We use symbols to represent the various components of a circuit in diagrams, so that electricians and scientists can draw circuits easily.
To draw electric circuits easily, scientists use standard symbols for the different components. These symbols make circuit diagrams neat and easy to understand. A cell is shown by two lines of different lengths - a long line and a short line - and a battery is shown by two or more cells joined together. A bulb is represented by a circle with a cross inside, a switch is shown by two circles joined by a gap or a breakable line, and connecting wires are shown by straight lines.
The direction of current is conventionally shown from the positive terminal of the cell to the negative terminal through the circuit. When the switch is closed, the circuit is complete and current flows, lighting the bulb. When the switch is open, the circuit is broken and the current stops. Learning these symbols is the first step in understanding and drawing circuits.
When electric current flows through a conductor, the conductor gets heated. This is called the heating effect of electric current. The heat is produced because the moving electrons collide with the atoms of the conductor, and some of the electrical energy is converted into heat energy. This heating effect is used in many devices like electric heaters, electric irons, electric kettles, geysers and electric bulbs.
The filament of an electric bulb is made of a thin tungsten wire, which gets heated to a high temperature and glows, producing light. In some bulbs, the filament is filled with an inert gas to prevent it from burning. When an electric current passes through a fuse wire, the fuse wire, which has a low melting point, melts and breaks the circuit, preventing damage to appliances. This is the safety role of a fuse. The heating effect also explains why the connecting wires of an electric circuit should not be short-circuited; if the live and neutral wires touch each other, a short circuit occurs, producing a large current and heat that can cause fires.
In 1820, Hans Christian Oersted discovered that a compass needle gets deflected when it is brought near a wire carrying electric current. This showed that electric current produces a magnetic effect. The magnetic effect of electric current is used to make electromagnets, which are magnets that work only when current flows through them. An electromagnet is made by winding an insulated copper wire around an iron core (like a nail) and passing current through it.
The strength of an electromagnet can be increased by increasing the number of turns of the coil, increasing the current, or using a stronger core. Electromagnets are used in electric bells, cranes for lifting heavy scrap iron, motors, loudspeakers and many other devices. In an electric bell, when current flows through the electromagnet, it attracts a soft iron hammer which strikes the bell; this demonstrates the magnetic effect of current. The magnetic effect is also the basis of the electric motor and the generator.
Some substances, when dissolved in water, conduct electricity, and when current passes through such solutions, chemical changes take place. This is called the chemical effect of electric current. For example, when current passes through a solution of copper sulphate, copper gets deposited on the electrode connected to the negative terminal of the battery. The process of depositing a layer of metal on another metal using electricity is called electroplating.
Electroplating is used for many purposes. Jewellery is coated with gold or silver to make it look attractive, iron objects are coated with zinc or chromium to prevent rusting, and tin is coated on iron sheets for cans. The chemical effect of electric current is also used to split water into hydrogen and oxygen (electrolysis) and to produce many industrial chemicals. This effect shows that current can cause chemical changes in conducting solutions.
| Effect of Current | Description | Example |
|---|---|---|
| Heating effect | Conductor gets heated when current flows | Electric heater, bulb, iron |
| Magnetic effect | Current produces magnetism | Electromagnet, electric bell |
| Chemical effect | Current causes chemical changes in solutions | Electroplating, electrolysis |
| Component | Symbol Description |
|---|---|
| Cell | Long and short line |
| Battery | Two or more cells together |
| Bulb | Circle with a cross |
| Switch (open) | Break in the wire with contacts |
| Wire | Straight line connecting components |
Electric current produces several important effects that are used in everyday life. The heating effect is used in bulbs, heaters and fuses, the magnetic effect is the basis of electromagnets, electric bells and motors, and the chemical effect is used in electroplating and electrolysis. Standard symbols help us draw circuits clearly, and the concept of a complete circuit is fundamental to all electrical devices. By understanding the effects of electric current, we can use electricity safely and efficiently and appreciate the science behind our everyday appliances.