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Oak National Academy
Oak National Academy
Teachers
Pupils
New
New
Year 11
OCR
Higher

Short circuits and earth wires

I can explain how electric circuits are wired in a home, with circuit breakers, fuses and earth wires for safety.

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New
New
Year 11
OCR
Higher

Short circuits and earth wires

I can explain how electric circuits are wired in a home, with circuit breakers, fuses and earth wires for safety.

Download all resources
Share activities with pupils

Lesson details

Key learning points

  1. A short circuit happens when a wire becomes loose and touches the wrong part of a circuit, or makes a new circuit.
  2. If a live wire touches the inside of a metal case, the metal case may become live.
  3. If there is too much current in an appliance, a fuse on the live wire in its plug melts and turns it off.
  4. From a live metal case, current flows along an earth and live wire, melts a fuse and turns the electricity off.
  5. 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

Demonstrate fuses and how an earth wire works, for example by following the method described in the additional information for this lesson.
Teacher tip

Equipment

power pack, heat resistant mat, leads and crocodile clips, thin resistance wire, lamp, and tin can

Licence

This content is © Oak National Academy Limited (2024), licensed on Open Government Licence version 3.0 except where otherwise stated. See Oak's terms & conditions (Collection 2).

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Starter quiz

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6 Questions

Q1.
The electricity from sockets and circuits in a home is called electricity.
Correct Answer: mains
Q2.
Which of the following are good electrical insulators?
Correct answer: air
iron
Correct answer: plastic
wet skin
Q3.
Which of the following are names of wires in appliances that are plugged into sockets at home?
Correct answer: live
negative
Correct answer: neutral
positive
Q4.
Which of the following causes pain or injury during an electric shock?
Correct answer: current
potential difference
resistance
Q5.
Which of the following statements about wires in a circuit is correct?
Correct answer: 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.
Q6.
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?
Correct answer: 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.
Correct answer: There is a large potential difference between the two wires.

Exit quiz

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6 Questions

Q1.
Some electrical appliances have two layers of electrical insulation: the plastic around the wires, and an insulating outer casing. This is called insulation.
Correct Answer: double
Q2.
The diagram shows three electric circuits. How many of these have a short circuit?
An image in a quiz
none of them
one
two
Correct answer: all of them
Q3.
Which of the following statements about a circuit breaker are correct?
Correct answer: It contains a switch.
Correct answer: It works faster than a fuse.
Correct answer: It contains an electromagnet.
If it switches on, it needs to be replaced.
A wire inside it melts if the current is too high.
Q4.
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
Correct answer: if the live wire comes loose and touches the metal casing
if the earth wire comes loose and touches the metal casing
Q5.
Which of the following is the earth wire of an appliance connected to?
Correct answer: the ground
the live wire
the neutral wire
Correct answer: the metal casing of the appliance
the insulation around the wires in the appliance
Q6.
Which of the following is the purpose of a fuse?
It creates a short circuit.
Correct answer: 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.

Additional material

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