# Electricity in the Home Unit 2b (i)

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• Created by: naomi2310
• Created on: 23-12-14 16:41
What current does 'Mains' supply use?
Alternating Current. This means the current is constantly changing direction. The frequency of AC is 50Hz
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What current does 'Battery' supply use?
Direct Current. The current keeps flowing in the same direction
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What is a CRO?
A cathode ray oscilloscope, a fancy voltmeter which shows a trace about how the voltage supply changes with time with an AC supply.
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What trace does a DC show on a CRO?
A straight line. Current is flowing in the same direction
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What does the vertical height of the AC trace show?
It shoews the input voltage at that point, by measuring the height of the trace you can find the potential difference of the AC supply.
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How do you calculate the frequency?
1/time period (s)
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Give 5 examples of electrical hazards in the home.
Choose any 5 from - Long Cables, Frayed Cables, Cables in contact with water or heat, Water near sockets, Damaged Plugs, Too many plugs in one socket, Lighting sockets without bulbs, Appliances without covers.
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What are the three wire colours and what are their names?
Brown - Live (LIVING), Blue - Neutral (WATER IS NEUTRAL), Earth - Green and Yellow (LAND AND SAND)
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What does the Earth Wire do? How does it protect you?
Earth wires are made to protect the wiring and for safety, they work with a fuse to prevent fire and shocks. It's attached to the metal casing of the plug and carries electric current to the earth (away from you) if something went wrong.
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Which wire does electricity flow out of?
The blue neutral wire.
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How does the Brown Wire Work?
Works in a mains supply and alternates between a high positive and negative voltage.
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Name 4 Safety features of three pin plugs.
1. The right coloured wire is connected to each pin, and firmly screwed in. 2. No bare wires showing. 3. Cable grip tightly fastened 4. Cable size, thick for less resistance and more current, thin for more resistance and less current.
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Why are the metal parts of plugs made from copper and brass?
They are very good conductors of electricity.
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Which material are the best insulators for plugs?
Plastics or rubbers are good insulators and flexible too.
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What is an RCCB? What does it do?
Residual Current Circuit Breakers. The RCCB detects a difference in current between the neutral and live wires, and cuts off the power. They work for even small current changes.
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What does a regular circuit breaker do?
When they detect a surge in current in a circuit they break the circuit by opening a switch. It protects the circuit from damage if too much current flows, like a fuse.
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What does a fuse do?
The fuse breaks the circuit if a fault in an appliance causes too much current to flow. This protects the wiring and the appliance if something goes wrong. The fuse contains a piece of wire that melts easily.
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What rating should my fuse have if my appliance works at 3A?
The fuse should have a 5A rating, fuses should be rated as near as possible but just higher than the normal operating current.
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As my cable thickness increases, my fuse rating...
Increases, the larger the current, the thicker the cable you need to carry it.
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Why don't things that have 'double insulation' need an earth wire?
Because the appliance will have a plastic case, which is 'earthed' already. This is known as a 'two core cable'
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What are the pros and cons of CB's and Fuses?
CB's are a lot more expensive than fuses, but can be easily reset, so are much more convenient than fuses. Fuses cost a fraction of the price, and prevent the risk of fire, however they need to be replaced often.
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## Other cards in this set

### Card 2

#### Front

What current does 'Battery' supply use?

#### Back

Direct Current. The current keeps flowing in the same direction

What is a CRO?

### Card 4

#### Front

What trace does a DC show on a CRO?

### Card 5

#### Front

What does the vertical height of the AC trace show?