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physics unit 2 > Electricity > Flashcards

Electricity Flashcards

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0
Q

Mains electricity is an AC supply. What is AC?

A

Current that repeatedly reverses it’s direction in successive cycles. Frequency is the number of cycles per second, which is 50 Hz in the UK. The voltage repeatedly changes from +/- 325 V

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1
Q

What is direct current?

A

Current in one direction only e.g. a torch

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2
Q

Read up on measuring alternating PD.

A

Yes.

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3
Q

When you plug a heater with a metal case into a wall socket, when you you do?

A

Earth the metal case automatically to stop the case becoming live if the live wire beaks and touches the case

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4
Q

The outer casing of plugs, sockets and cables are made of what?

A

Electrical insulators because they contain live wires

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5
Q

Most mains appliances are connected via a wall socket in the mains using a cable and a three-pin plug

A

Yes.

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6
Q

What are sockets made from?

A

Stuff plastic materials with wires inside (see diagram)

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7
Q

The earth wires of a circuit in a socket are connected to where?

A

The ground at your home

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8
Q

What is the longest pin of a plug designed to make contact with?

A

The earth wire of a wall socket circuit so when you plug in an appliance with a metal case the case is automatically earthed

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9
Q

Plugs have three wires with different colours. What are they?

A

Live wire = brown
Neutral wire = blue
Earth wire = green and yellow

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10
Q

Plugs have stiff plastic materials which the pins stick out of. They can not touch each other when the plug is sealed. The pins are made of brass but not copper. Why?

A

Copper is a better conductor but brass is still very good. Brass is harder than copper and does not rust or oxidise.

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11
Q

Why does the plug contain a fuse between the live pin and the live wire?

A

So if too much current passes through it, the fuse will melt and cut off the live wire

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12
Q

What do cables consist of?

A

Two or three insulated copper wires surrounded by an outer layer of rubber. Copper is used because it is a good electrical conductor and bends easily and plastic is used to cover them because it is a good electrical insulator so anybody touching the cable will not receive an electric shock.

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13
Q

What kinds of appliances are two-core cables used for?

A

Those with a plastic case that are double-insulated

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14
Q

Why are thicker wires used where lots of current flows through them?

A

To make the resistance smaller to minimise the heating effect of the current

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15
Q

What does a fuse contain?

A

A thin wire that heats up and melts if too much current passes through it

16
Q

What does the rating of a fuse tell you?

A

How much current can pass through it without melting the fuse wire

17
Q

The heating affect of the current could cause a fire.

A

Yes.

18
Q

What is a circuit breaker?

A

An electromagnet that opens when there is a fault to stop current flowing in the live wire. If the current in the wire is too large, the magnetic field of the electromagnet pulls the switch apart.

19
Q

What are circuit breakers better than fuses?

A

They work faster and can be reset more quickly

20
Q

What is a Residual Current Circuit Breaker (RCCB)?

A

A circuit breaker that cute off current in the live wire if it is a different current to the neutral wire. It is more sensitive than a normal circuit breaker and can be used where there is no earth wire

21
Q

Power = energy transferred/time

A

P = E/T

22
Q

Each electron in a circuit transfers a small amount of energy from each electron. The PD across a component is the energy transferred to the appliance by each coulomb of charge that passes through it

A

Yes.

23
Q

Power supplied is therefore equal to the rate of flow of charge x the energy transfer per unit of charge

A

So power = current x voltage

24
Q

What are the most common types of fuse?

A

3A, 5A and 13A

25
Q

When a resistor is connected to a battery, electrons are made to pass through it. Each electron collides with the vibrating metal ions in the resistor and transfers energy to them so the resistor gains energy and vibrates even more to become hotter.

A

Yes.

26
Q

Because power x time = pd x current x time, energy transferred = pd x charge

A

Yes.

27
Q

If you fuse blows or a circuit breaker breaks you should…?

A

Switch off the appliance and get out a qualified electrician

28
Q

Too many appliances connects in a socket may result in overheating.

A

Yes.

physics unit 2 (4 decks)

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