Simple Circuits and Conductors
FoundationA complete circuit needs a power source, wires, a switch and an appliance. Metals are conductors; plastic and dry wood are insulators. Test materials with a battery circuit, and always remember: never touch electrical things with wet hands.
- A complete circuit has a power source, wires, a switch and an appliance.
- Metals are conductors; plastic, rubber, glass and dry wood are insulators.
- Test materials across a gap in a circuit: light means conductor.
文體小知識：趣味實驗說明文帶我們動手接駁電路做實驗，導電的秘密就在指掌之間。
§Text Passage
1For a bulb to light up, the current must travel a complete loop — that loop is a circuit. A simple circuit has four parts: the battery providing energy (the power source), the wires letting the current flow, the switch controlling whether the current flows, and the bulb that uses the energy (the appliance). Only with all four in place does the bulb light when the switch closes.
2A wire shows how conductors and insulators share the work: the copper strands inside let current pass — a conductor; the plastic coat outside protects us from shocks — an insulator. Most metals conduct well, such as copper, iron and aluminium; plastic, rubber, glass and dry wood do not conduct and are used to block current.
3Test materials with a little experiment: connect a battery, wires and a small bulb into a circuit, leaving a gap in one wire, then touch both ends of the test material across the gap. If the bulb lights, the material conducts — a conductor; if not, it is an insulator. Try a paper clip, a pencil lead, a plastic ruler and an eraser, and record the results in a table.
4Electrical safety must always be remembered: never touch appliances or sockets with wet hands; never push metal objects into sockets; if an appliance smokes or smells strange, tell an adult at once and cut the power; stop using batteries that get hot or leak. Experiments use low-voltage batteries only — never mains power or wall sockets.
1Summary 重點摘要
A complete circuit needs a power source, wires, a switch and an appliance. Metals are conductors; plastic and dry wood are insulators. Test materials with a battery circuit, and always remember: never touch electrical things with wet hands.
2Vocabulary cards Vocabulary
The complete, closed path that an electric current follows.
The part providing electrical energy, usually a battery in experiments.
The part that controls the current: closed lets it flow, open stops it.
A material that lets current pass easily, such as the metals copper, iron and aluminium.
A material that blocks current, such as plastic, rubber and dry wood.
The electricity flowing in a circuit that lights bulbs and turns motors.
A device that uses electrical energy to work, such as a bulb or small motor.
A break in the circuit where current cannot pass and the bulb stays dark.
The safe source for experiments, such as one to three dry cells — never mains power.
3Step by step Steps
- Step 1: Learn the four parts of a circuitA complete circuit has four parts: a power source, wires, a switch and an appliance. A torch shows them best: the battery is the power source, the button is the switch that opens and closes the path, the bulb is the glowing appliance, and the metal strip and spring inside act as the wires. Knowing the four parts makes wiring a circuit much easier. With an adult's help, take apart an old torch and see where each of the four parts sits and what it looks like.
- Step 2: Connect a complete circuitElectric current must flow round a complete loop for an appliance to work. Link the battery, switch and bulb holder with wires into one circle; close the switch and the current flows, so the bulb lights; open the loop anywhere and the current stops, so the bulb goes dark. A circuit must be closed to carry electricity — that is the key rule. Wind the wires firmly round the terminals when connecting; loose joints are the most common source of circuit faults.
- Step 3: Troubleshoot a dark bulbWhen the bulb does not light, stay calm and check in order to find the cause. Check whether the battery has power, whether any wire has come loose, whether the bulb is screwed in tightly, and finally whether the switch is closed. Retest after each check. This habit of troubleshooting step by step helps in other experiments too. Check item by item in a fixed order so nothing is missed; this way of thinking serves every experiment you do.
- Step 4: Test whether materials conductSome materials let current pass; others do not. Leave a gap in the circuit and touch a paper clip across the two sides — the bulb lights, proving that iron conducts electricity and is a conductor; swap in a plastic ruler and the bulb stays dark, proving that plastic does not conduct and is an insulator. Judging by light or no light makes the results obvious at a glance. The human body and graphite conduct too — graphite is the material of pencil lead; test a pencil lead and the bulb lights as well.
- Step 5: Record and sort conductors and insulatorsRecord the test results systematically to draw out the pattern. Write each material and its result in a table: the paper clip conducts, pencil lead conducts, the plastic ruler does not, the dry wood strip does not. Comparing the table, we find that metals are mostly conductors while plastics and dry wood are mostly insulators. Recording and sorting are key steps in scientific inquiry. The table's pattern lets us reason further: a wire has a copper core and a plastic coat — the division of conducting and insulating.
- Step 6: Follow electrical safety rulesElectrical experiments demand safety first. Use dry cells only — their low voltage is safe — and never experiment with mains sockets; dry your hands fully before touching appliances, because wet hands conduct electricity easily; if a socket is loose or a wire damaged, never touch it — tell an adult at once. Safety always comes first. If an appliance at home acts oddly, getting hot or smelling strange, cut the power first and then ask an adult to handle it.
4Diagrams Diagrams
5Worked example Example
Example: Yau wired up a circuit and closed the switch, but the bulb does not light. The battery is brand new. Give three possible causes and how to check each.
- Cause one: poor contact between the wires and the battery or holder — press each connection firm and try again.
- Cause two: the bulb is loose or its filament is broken — screw it in gently, or swap in a known good bulb to test.
- Cause three: the switch is open or wrongly placed — check the switch, and if needed test by briefly touching the two wires together under an adult's guidance, separating them again at once.
- After checking and fixing each item, close the switch again; the bulb lights and the circuit is complete.
- Answer: Likely causes are poor contact, a loose or broken bulb, or an open switch; check and fix each in turn, and once the circuit is closed and complete the bulb will light again — remembering throughout to use dry cells only.
6Common mistakes Mistakes
7Quick check Quick check
Q1What four parts make up a simple circuit?
Q2Why does a wire have plastic outside and metal inside?
Q3How do we test whether a material conducts electricity?
Q4Which are conductors: copper wire, a dry wood strip, an aluminium can, a plastic ruler?
Q5Why must we never touch appliances with wet hands?
8Recap Recap
- A complete circuit has a power source, wires, a switch and an appliance.
- Metals are conductors; plastic, rubber, glass and dry wood are insulators.
- Test materials across a gap in a circuit: light means conductor.
- If a bulb stays dark, check the battery, connections, bulb and switch in turn.
- Safety first: dry hands only, and low-voltage batteries for experiments.