PHYSICS · Stage 7 · Chapter 4: Electricity
Physics 4.2 Electric circuits — Circuit Symbols, Cells, Switches and Lamps
5 min read 6 parts Lesson 2 of 6
Lesson summary
4.2 Electric circuits — Circuit Symbols, Cells, Switches and Lamps — Alhussan International Academy — Physics (Stages 7–9) notes: Draw circuits using standard symbols and test whether materials are conductors or insulators.Uses — televisions, movie projectors and loudspeakers run…
- Circuit diagram
- Cell and battery
- Joining cells
- Requirements
- Torch circuit
- Short circuit
Part 1 of 6Why circuits matter and how we draw them
- Uses — televisions, movie projectors and loudspeakers run on electricity, and hospitals use machines that run on electricity to keep people alive, such as the anaesthesia machine in an operating theatre.
- They all contain electric circuits made of electrical components.
- Circuit symbols — drawing pictures of components would take a long time, so standard symbols show which components are in a circuit.
- Circuit diagram = a diagram that joins circuit symbols to show how the components are connected.
Part 2 of 6Components and symbols
| Component | Job in the circuit |
|---|---|
| Wire | Connects the components together |
| Cell | Provides the push (energy) to move charge |
| Battery of cells | Two or more cells joined together |
| Lamp | Transfers electrical energy to light and heat |
| Open switch | Breaks the circuit so no current flows |
| Closed switch | Completes the circuit |
| Buzzer | Transfers electrical energy to sound |
| Motor | Transfers electrical energy to movement |
- Cell and battery — many people call a cell a battery, but in physics a battery contains two or more cells.
- Terminals — a cell has a positive and a negative terminal.
- On the circuit symbol the long line represents the positive terminal and the short line the negative terminal.
- Joining cells — in a battery, do not connect two positive terminals or two negative terminals together, or it will not work.
Part 3 of 6A complete circuit
- Requirements — a complete circuit needs a source of energy (a cell), a conducting path (wires) with no gaps, and a component that does something useful (a lamp).
- Torch circuit — a lamp, a battery, some wire and a switch make a very simple circuit like the one in a torch.
- When the switch is open it is a break in the circuit, so no current flows and the lamp is off.
- When the switch is closed the circuit is complete and the lamp lights.
- Short circuit — connecting the lamp straight across the cell with only a wire lets a very large current flow, which can overheat the wire and the cell.
Part 4 of 6Testing conductors and insulators
- Conductor = an object or material that conducts electricity easily.
- Insulator = an object or material that does not conduct electricity easily.
- Test — Mawar and Harta set up a torch-like circuit with a gap in it and put different materials across the gap.
- If the bulb lights up, the material is a conductor.
- If the lamp stays off, it is an insulator.
- Variables — the material is the independent variable, whether the lamp lights is the dependent variable, and the cell, lamp and wires stay the same.
| Conductors | Insulators |
|---|---|
| Metal spoon, coin, aluminium foil | Paper, plastic spoon, wood, string |
Part 5 of 6Not only metals conduct
- Common idea — some people think only metals conduct electricity, but that is not correct.
- Graphite — it is a form of carbon found in the centre of a pencil, and it conducts electricity while the wood around it does not.
Part 6 of 6Conductors and insulators together in a cable
- Copper wire — the wires for electrical appliances are made of copper, a metal conductor that carries the current.
- Plastic covering — it is an insulator that keeps the current in the wire and keeps people safe.
- Bare wires would be very dangerous because you could get an electric shock if you touched them.
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