What this chapter is about
This chapter introduces you to how electricity flows and what parts make up an electric circuit. You will learn why a bulb lights up when you press a switch and why it goes off when the circuit breaks.
Electricity powers many things we use every day — fans, lights, televisions, mobile phones. Understanding circuits helps you see how these devices work. It also teaches you to stay safe around electricity.
After studying this chapter, you should be able to draw simple circuits, identify their parts, and explain why some materials let electricity pass while others do not.
Key ideas
- An electric circuit is a closed path through which electric current can flow.
- A circuit needs a source of electricity (like a cell or battery), connecting wires, and a device (like a bulb or buzzer) to work.
- A switch controls the flow of current by opening or closing the circuit.
- When the circuit is closed (complete), current flows and the bulb glows. When the circuit is open (broken), current stops.
- Materials that allow electricity to pass through them are called conductors. Metals like copper, iron and aluminium are good conductors.
- Materials that do not allow electricity to pass are called insulators. Rubber, plastic, wood and glass are common insulators.
- A cell has two terminals: the positive terminal (the cap with a small bump) and the negative terminal (the flat metal base).
- Circuit diagrams use symbols to represent cells, bulbs, switches and wires in a neat way.
Formulas and facts to remember
- Electric current is the flow of electric charge through a conductor.
- Cell is a device that provides electrical energy by converting chemical energy.
- Battery is two or more cells joined together.
- Conductor allows current to pass easily (examples: copper wire, iron nail, steel spoon).
- Insulator blocks current (examples: plastic comb, rubber eraser, wooden stick).
- Open circuit means the path is broken and no current flows.
- Closed circuit means the path is complete and current flows.
- The direction of current in a circuit diagram is shown from the positive terminal to the negative terminal of the cell.
Worked examples
Example 1: Building a simple circuit
Riya has one cell, two wires, a small bulb and a switch. She connects one wire from the positive terminal of the cell to one end of the switch. Another wire goes from the other end of the switch to the bulb. A third wire joins the bulb back to the negative terminal of the cell.
When Riya closes the switch, the path is complete. Current flows from the cell, through the switch, through the bulb, and back to the cell. The bulb glows.
When she opens the switch, the path breaks. Current stops. The bulb does not glow.
Example 2: Testing conductors and insulators
Arjun sets up a circuit with a cell, a bulb and two wires. He leaves a gap between the two wire ends. He places different objects in the gap to test them.
- He places a steel key. The bulb glows. Steel is a conductor.
- He places a plastic ruler. The bulb does not glow. Plastic is an insulator.
- He places an aluminium foil strip. The bulb glows. Aluminium is a conductor.
Example 3: Drawing a circuit diagram
Draw a circuit with one cell, one bulb and one closed switch.
Use the symbol for a cell (one long line for positive, one short line for negative), a circle with a cross for the bulb, and a simple line with a gap that closes for the switch. Connect them in a loop with straight lines for wires. Since the switch is closed, the loop is complete.
Common mistakes
- Thinking that current gets used up inside the bulb → Current flows through the bulb and returns to the cell; it is not consumed.
- Believing plastic-coated wires are insulators → The plastic coating is an insulator, but the metal wire inside is a conductor; current flows through the metal.
- Connecting both wires to the same terminal of the cell → A circuit needs connections to both the positive and negative terminals to form a closed path.
- Assuming all liquids are insulators → Some liquids like salt water conduct electricity; pure water is a poor conductor, but tap water contains salts.
- Forgetting that a single break anywhere in the circuit stops current → Even if only the switch is open, the whole circuit stops working.
Quick revision
- A circuit must be closed (complete) for current to flow.
- Conductors let current pass; insulators block it.
- A cell has a positive terminal and a negative terminal.
- A switch opens or closes a circuit.
- Use symbols to draw neat circuit diagrams.