Electricity Circuits and their Components
Flick a switch and a bulb lights up — because a complete circuit lets current flow. This Class 7 Curiosity chapter explains the components of an electric circuit, how to draw them with symbols, the difference between conductors and insulators, and the heating and magnetic effects of electric current.
Learning objectives
- Identify the components of a circuit.
- Draw circuits using symbols.
- Distinguish conductors and insulators.
- Describe heating and magnetic effects of current.
Key concepts
Electric circuit and its components
An electric circuit is a complete path along which electric current flows. Its main components are a cell or battery (the source), connecting wires, a bulb or other device, and a switch to open or close the path. Current flows only when the circuit is complete, called a closed circuit.
Cells, batteries and switches
A cell stores chemical energy and provides electricity; two or more cells joined together make a battery. A switch is a device that closes the circuit to let current flow (on) or breaks it to stop the flow (off). When the switch is open the bulb does not glow.
Circuit symbols and conductors
To draw circuits neatly, we use standard symbols for the cell, bulb, switch and wires. Materials that allow current to pass are conductors, such as metals; materials that do not are insulators, such as rubber, plastic and wood. Wires are made of conductors covered with insulators for safety.
Effects of electric current
Electric current produces useful effects. The heating effect makes a wire hot when current passes, used in heaters and bulbs. The magnetic effect means a current-carrying wire behaves like a magnet; a coil of wire with current becomes an electromagnet, used in electric bells and many machines.
Key definitions
- Electric circuit
- A complete path through which electric current can flow.
- Battery
- Two or more cells joined together to supply electricity.
- Conductor
- A material that allows electric current to pass through it.
- Electromagnet
- A coil that acts as a magnet when current flows through it.
Solved examples
Q1. When does a bulb in a circuit glow?
Solution: When the circuit is closed (complete) so current can flow.
Q2. Is copper a conductor or an insulator?
Solution: A conductor; metals conduct electricity.
Q3. Name the effect used in an electric heater.
Solution: The heating effect of electric current.
Common mistakes to avoid
- Thinking a bulb glows even when the circuit is open.
- Confusing a single cell with a battery.
- Believing plastic and rubber conduct electricity.
- Mixing up the heating effect with the magnetic effect.
Electricity Circuits and their Components — MCQ Quiz
10 questions with instant feedback. Use number keys 1–4 to answer.
Current flows only when the circuit is:
Practice questions
Short answer
What is an electric circuit?
A complete path through which current can flow.
Give one conductor and one insulator.
Conductor: copper; insulator: rubber.
What is an electromagnet?
A coil that acts as a magnet when current flows through it.
Long answer
Describe the components of a simple electric circuit and the role of each.
A simple electric circuit needs a few components working together to form a complete path for current. The cell or battery is the source that supplies electricity. Connecting wires, made of a conducting metal, carry the current around the circuit. A device such as a bulb uses the current to do something useful, like giving light. A switch is included to open or close the circuit: when the switch is closed the path is complete and current flows, so the bulb glows; when it is open the path is broken and the bulb goes off. Current flows only when the whole circuit is closed.
Explain the heating and magnetic effects of electric current with examples.
Electric current produces several effects, two of which are especially useful. The heating effect occurs because current makes a wire hot as it passes through; this is used in electric heaters, irons, geysers and the filaments of bulbs. The magnetic effect means that a wire carrying current behaves like a magnet and can deflect a nearby compass needle. When the wire is wound into a coil and current flows, it becomes an electromagnet — a magnet that can be switched on and off — which is used in electric bells, cranes that lift iron, and many electrical machines.
HOTS (Higher Order Thinking)
Why are the handles of electricians' tools covered with rubber or plastic?
Because rubber and plastic are insulators; they prevent current from passing into the user, keeping them safe.
An electromagnet can be switched off but an ordinary magnet cannot. Why is this useful in a scrapyard crane?
The crane can pick up iron when current flows and drop it by switching off the current, controlling the magnetism at will.
Quick revision
Revision notes
- Closed circuit = current flows; open circuit = no flow.
- Cell is the source; joined cells = battery.
- Conductors (metals) pass current; insulators (rubber, plastic) don't.
- Current effects: heating (heaters) and magnetic (electromagnet).
Key takeaways
- A bulb glows only in a complete circuit.
- Conductors carry current; insulators block it.
- Current can heat and can act like a magnet.
Frequently asked questions
Why doesn't a bulb glow when the switch is off?
The circuit is open, so current cannot flow.
What is the difference between a cell and a battery?
A battery is two or more cells joined together.
What is an electromagnet used for?
Electric bells, cranes that lift iron, and many machines.