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.
- Year 11
- AQA
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.
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.
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
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.
Equipment
power pack, heat resistant mat, leads and crocodile clips, thin resistance wire, lamp, and tin can
Licence
Lesson video
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Prior knowledge starter quiz
6 Questions
Q1.The electricity from sockets and circuits in a home is called electricity.
Q2.Which of the following are good electrical insulators?
Q3.Which of the following are names of wires in appliances that are plugged into sockets at home?
Q4.Which of the following causes pain or injury during an electric shock?
Q5.Which of the following statements about wires in a circuit is correct?
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?
Assessment exit quiz
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.
Q2.The diagram shows three electric circuits. How many of these have a short circuit?
