Electricity – JSS2 Intermediate Science Lesson Note (Third Term)

Electricity is a form of energy produced by the flow of electric charges, called electrons, through a material such as a wire.

Behavioural objectives

1. Define electric current and voltage.
2. State the units and measuring instruments for current and voltage.
3. Identify the parts of a simple electric circuit.
4. Define conductors and insulators and give examples of each.
5. Explain why wires are covered with plastic or rubber.

What is electric current?

Electric current is the rate at which electric charges flow past a point in a circuit.

• Water comparison: still water does nothing, but flowing water can turn a waterwheel or fill a bucket.
• What flows: tiny particles called electrons move through the wire.
• Unit: the ampere (amp). The symbol is A.
• Instrument: the ammeter measures how much current is flowing.
• How it is connected: an ammeter is connected in series, in the same path as the current.

What is voltage?

Voltage, also called potential difference, is the push that drives electric charges through a conductor.

• Water comparison: a pump or a high tank gives water the pressure to flow. Voltage does this for electric charges.
• Sources of voltage: cells, batteries and the wall socket.
• Without voltage: the charges do not flow in one direction, so the bulb does not light.
• Unit: the volt. The symbol is V.
• Instrument: the voltmeter measures voltage.
• How it is connected: a voltmeter is connected in parallel, across the part being measured.

What is the difference between current and voltage?

Current is the flow of charges, while voltage is the push that makes them flow.

What is a simple electric circuit?

A simple electric circuit is a complete closed path along which electric current can flow.

Parts of a simple circuit

• Cell or battery: supplies the voltage that pushes the charges.
• Connecting wires: carry the current round the circuit, usually copper.
• Bulb: uses the electrical energy and gives out light.
• Switch: opens or closes the circuit to turn the current off or on.

How does a bulb light in a circuit?

1. The cell provides a voltage.
2. The voltage pushes electrons through the wires.
3. The current passes through the bulb.
4. The bulb lights up.
5. If the circuit is broken anywhere, the current stops and the bulb goes off.

What are conductors?

Conductors are materials that allow electric current to pass through them easily.

• Why they conduct: they have many free electrons that move easily.
• Common conductors: most metals are good conductors.

Examples of conductors

• Copper: the most common metal for house wiring because it conducts very well and is fairly cheap.
• Aluminium: used for the large overhead power lines seen along roads.
• Silver: the best conductor of all metals, but too costly for wiring.
• Gold: a very good conductor, but also too costly for house wiring.
• Iron: a metal that conducts electricity, though not as well as copper.
• Graphite: a non-metal found in pencil lead that conducts electricity.
• Salt water: conducts electricity because of the salt dissolved in it.
• The human body: conducts electricity, so we must avoid electric shock.

What are insulators?

Insulators are materials that do not allow electric current to pass through them.

• Why they block current: they have almost no free electrons.
• Why we need them: they protect us from electric shock.

Examples of insulators

• Plastic: covers wires and makes the casing of sockets and switches.
• Rubber: covers wires and makes handles for screwdrivers and pliers.
• Dry wood: a dry wooden stick does not conduct electricity.
• Glass: does not conduct electricity.
• Ceramics: used on power poles to stop the wires touching the pole.
• Air: usually an insulator, so electricity does not jump out of sockets.

What is the difference between conductors and insulators?

Conductors carry electricity, while insulators block it and keep us safe.

How do we stay safe around electricity?

We stay safe by keeping our bodies away from live wires and by using insulators.

• Covered wires: copper wires are wrapped in plastic or rubber so we can touch them safely.
• Bare wires: never touch a bare or damaged wire.
• Water: keep water away from sockets and do not touch switches with wet hands.
• Fallen cables: keep away from fallen power lines.
• Tools: use tools with rubber or plastic handles when working on electrical items.

Evaluation

1. What is the difference between electric current and voltage?
2. Which instrument measures current in amperes?
3. Why are electrical wires usually covered with plastic or rubber?
4. Name two metals that are good conductors.
5. List the four parts of a simple electric circuit.

Assignment

Make a table of five conductors and five insulators found at home. Give one use of each material.