# P4c: Safe Electricals

This item investigates electricity. Safety is a major requirement when electricity is used in a medical situation. Here the principles of fuses and earthing are studied.

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How does electric current flow?
Electric current flows in a closed path called an electric circuit.
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How can resistors be used to change the current?
Resistors slow the current flow down.
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Describe how variable resistors can be used to change the current.
Longer wires give less current, likewise thinner wires.
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What is a rheostat?
A variable resistor.
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What is resistance measured in?
Ohms (Ω)
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What are the three wires in a plug?
brown-live, blue-neutral, yellow/green-earth.
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What can not become live?
An earthed conductor.
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Reason for the use of fuses and circuit breakers. (resettable fuses)
To protect electrical circuits and appliances. Residual-current devices, RCDs, protect some circuits. They detect a difference in the current between the live and neutral wires. RCDs work much faster than fuses do.
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What type of appliances don't need insulating?
Double insulated appliances.
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Explain how variable resistors can be used to change the current (resistance)
longer and shorter wires have more resistance
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what is the equation for resistance?
voltage/current
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Describe the relationships between current voltage and resistance. (2)
For a given resistor, current increases as voltage increase (vise versa) For a fixed voltage, current decreases as resistance increase (vise versa)
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Describe the functions of the live, neutral and earth wires.
Live - carries the high voltage, Neutral - completes the circuit, Earth - safety wire to stop the appliance becoming live
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Explain how a wire fuse reduces the risk of a fire; if the appliance develops a fault (4)
Too large a current causes the fuse to melt, preventing flow of current, prevents flex overheating and causing fire, prevents further damage to appliance.
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What is the equation for power?
Voltage x Current.
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Why do double insulated appliances not need earthing?
The appliance is a non conductor and can not become live.
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Explain how the combination of a wire fuse and earthing protects people.
Many electrical appliances have metal cases, the earth wire creates a safe route for the current to flow through if the live wire touches the casing.
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What is the equation to work out a suitable fuse?
Current = power/voltage
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## Other cards in this set

### Card 2

#### Front

How can resistors be used to change the current?

#### Back

Resistors slow the current flow down.

### Card 3

#### Front

Describe how variable resistors can be used to change the current.

### Card 4

#### Front

What is a rheostat?

### Card 5

#### Front

What is resistance measured in?