Electricity and Circuits

What you'll learn

• How electricity flows in a circuit — what is needed.
• Parts of a circuit: cell, bulb, switch, wires.
• Difference between conductors and insulators.
• Series and parallel circuits basics.
• Safety with electricity.

Key concepts

Sources of electricity

• Cell: a device that converts chemical energy to electrical energy; has a positive (+) and negative (−) terminal.
• Battery: two or more cells connected together.
• Other sources: generators, solar panels, fuel cells.

Cell symbol:

• Long thin line = positive (+) terminal.
• Short thick line = negative (−) terminal.

Electric circuit

• An electric circuit is a complete, closed path through which electric current can flow.
• Electric current: flow of electric charge (electrons) through a conductor.
• Current flows from the positive terminal of the cell, through the circuit, to the negative terminal.

Requirements for current to flow:

1. A complete, unbroken (closed) circuit — any break stops current.
2. A source of electricity (cell/battery).
3. Conducting path (wires, components).

Components and their functions

Switch:

• Open switch: breaks the circuit → current cannot flow → bulb off.
• Closed switch: completes the circuit → current flows → bulb lights up.

Conductors and insulators

• Copper is the most common material for wires — excellent conductor; flexible; not too expensive.
• Rubber and plastic used to insulate wires — prevents electric shocks.
• The human body is a conductor → electricity can flow through us → never touch live wires.

Testing conductors and insulators:

• Make a circuit with a bulb and cell with two free wire ends.
• Touch the object to be tested between the free ends.
• Bulb glows → object is a conductor.
• Bulb doesn't glow → object is an insulator.

Series and parallel circuits (introduction)

Series circuit:

• All components connected in one loop, end-to-end.
• Same current flows through all components.
• If one component fails → whole circuit breaks → all bulbs go out.
• Example: old-style Christmas lights.

Parallel circuit:

• Components connected in separate branches.
• Same voltage (potential difference) across each branch.
• If one component fails → other branches still work.
• Example: household wiring — appliances work independently.

Electrical safety

• Never touch electrical equipment with wet hands.
• Never insert fingers or objects into electric sockets.
• Always use insulated (plastic/rubber covered) wires.
• Switch off appliances before repairing.
• Fuse: a safety device — thin wire melts if current is too high, breaking circuit and preventing fire or damage.
• Don't overload sockets — too many appliances → too much current → danger.
• Lightning conductor: tall metal rod on buildings; provides safe path for lightning to reach earth.

Quick check

• What is needed for an electric current to flow?
• What is the difference between a conductor and an insulator? Give two examples of each.
• Explain what happens when a switch is opened in a circuit.
• Compare series and parallel circuits — give one advantage of each.
• Why is copper used for electric wires and plastic used to cover them?

Open the Practice tab for graded questions on Electricity and Circuits.