Starter quiz
- The electricity from sockets and circuits in a home is called ______ electricity.
- 'mains' ✓
- Which of the following are good electrical insulators?
- air ✓
- iron
- plastic ✓
- wet skin
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- Which of the following are names of wires in appliances that are plugged into sockets at home?
- live ✓
- negative
- neutral ✓
- positive
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- Which of the following causes pain or injury during an electric shock?
- current ✓
- potential difference
- resistance
-
- Which of the following statements about wires in a circuit is correct?
- The wires usually have much less resistance than the components. ✓
- The wires usually have similar resistance to the components.
- The wires usually have much more resistance than the components.
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- A person touches a live wire with one hand and a neutral wire with the other hand. Which of these statements explain why they get an electric shock?
- A current flows between the two wires. ✓
- There is a large resistance between the two wires.
- There is a small potential difference between the two wires.
- There is a large potential difference between the two wires. ✓
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Exit quiz
- Some electrical appliances have two layers of electrical insulation: the plastic around the wires, and an insulating outer casing. This is called ______ insulation.
- 'double' ✓
The diagram shows three electric circuits. How many of these have a short circuit?- none of them
- one
- two
- all of them ✓
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- Which of the following statements about a circuit breaker are correct?
- It contains a switch. ✓
- It works faster than a fuse. ✓
- It contains an electromagnet. ✓
- If it switches on, it needs to be replaced.
- A wire inside it melts if the current is too high.
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- When does current flow in the earth wire of an appliance that has a metal outer casing?
- whenever the appliance is running
- always, whether the appliance is switched on or off
- if the live wire comes loose and touches the metal casing ✓
- if the earth wire comes loose and touches the metal casing
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- Which of the following is the earth wire of an appliance connected to?
- the ground ✓
- the live wire
- the neutral wire
- the metal casing of the appliance ✓
- the insulation around the wires in the appliance
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- Which of the following is the purpose of a fuse?
- It creates a short circuit.
- It breaks the circuit if the current is too large. ✓
- It is used as a switch to turn a circuit on and off.
- It provides a low resistance path for current to flow to earth.
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Worksheet
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Presentation
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Video
Lesson Details
Key learning points
- A short circuit happens when a wire becomes loose and touches the wrong part of a circuit, or makes a new circuit.
- If a live wire touches the inside of a metal case, the metal case may become live.
- If there is too much current in an appliance, a fuse on the live wire in its plug melts and turns it off.
- From a live metal case, current flows along an earth and live wire, melts a fuse and turns the electricity off.
- Domestic circuits with excessive current are turned off by circuit breakers in a consumer box to prevent fire.
Common misconception
A short circuit is a circuit that doesn’t work.
Demonstrate several short circuits and provide opportunity for pupils to describe what they are in their own words.
Keywords
Short circuit - a complete circuit with a very small resistance, often caused by a loose wire
Double insulation - two layers of electrical insulation, including the outer casing of an appliance
Fuse - a thin wire that melts when a dangerously large current flows through it
Earth wire - a wire connected between a metal casing and the ground (0 V)
Circuit breaker - a switch that is turned off by an electromagnet when a dangerously large current flows through it
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