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Physics - Unit Two > Mains Electricity and Appliances > Flashcards

Mains Electricity and Appliances Flashcards

1
Q

What is d.c.?

A

Direct current means that the current always moves in one direction.

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2
Q

What are two things that supply d.c.?

A

Cells and batteries

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3
Q

What is a.c.?

A

Alternating current is a current that is constantly changing direction.

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4
Q

Is the mains supply a.c. or d.c.?

A

A.c.

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5
Q

What is the frequency of mains current and what is its voltage?

A

Its frequency is 50Hz and its voltage is 230V.

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6
Q

What is a CRO?

A

A cathode ray oscilloscope allows us to see how the voltage of an electricity supply changes over time.

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7
Q

What does a d.c. supply look like in a CRO? How can you work out the current’s voltage from it?

A

A straight horizontal line. The voltage of the current is just the distance from the straight line trace to the centre line.

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8
Q

What does an a.c. supply look like in a CRO? How can you work out the current’s voltage from it?

A

It goes up and down. The vertical height of the peak to the centre line denotes the voltage.

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9
Q

How can one work out the frequency of a wave from an CRO?

A

1
Hz = —————-
time period (s)

The time period is found by measuring the distance between the peaks of the waves.

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10
Q

How are long cables dangerous?

A
  • You can trip up

* They can overheat and cause fires if bundled up

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11
Q

How are frayed cables dangerous?

A

Exposed wires could give you an electric shock.

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12
Q

How is having too many plugs in one socket dangerous?

A

The socket could overheat and cause a fire.

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13
Q

How is having cables in contact with something hot dangerous?

A

The cables could overheat and cause a fire.

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14
Q

Why is having water near sockets of cables dangerous?

A

Water conducts electricity so could give you an electric shock or electrocute you if they were to come into contact.

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15
Q

Why is job in plugs into sockets dangerous?

A

You could get an electric shock or be electrocuted.

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16
Q

Why is using a damaged plug dangerous?

A

Exposed live parts could give you an electric shock.

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17
Q

How are empty light bulb sockets dangerous?

A

Touching the socket could give you an electric shock.

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18
Q

How is using appliances without their covers on dangerous?

A

The exposed live parts could give you an electric shock.

19
Q

What is a three core cable?

A

A cable containing three individually plastic coated copper wires:

  • The live wire
  • The neutral wire
  • The earth wire
20
Q

What colour is the love wire?

A

Brown

21
Q

What does the live wire do?

A

It alternates between a positive and negative voltage in a mains supply.

22
Q

What colour is the neutral wire?

A

Blue

23
Q

What is the voltage of the neutral wire?

A

0V

24
Q

What colour is the earth wire?

A

Yellow and green

25
Q

What is the role of the earth wire?

A

To carry electricity to earth and away from you if something goes wrong an one of the other wired touches the metal case.

26
Q

What is a two/core cable?

A

A cable that doesn’t have an earth wire.

27
Q

When looking at a plug, what should you check about the wiring?

A
  • That the right coloured wire is connected to each pin and is firmly screwed in.
  • No bare wires are showing.
  • The cable grip is fastened over the cable outer layer.
28
Q

What wire should be connected to the top pin in a plug?

A

The earth wire.

29
Q

What wire should be connected to the left hand pin in a plug?

A

The neutral wire.

30
Q

What wire should be connected to the right hand pin in a plug?

A

The live wire

31
Q

What materials are good for the metal parts of a plug?

A

Copper or brass because they’re very conductive.

32
Q

What should the case, cable grip and insulation in a plug be made of?

A

Rubber or plastic because they’re good insulators and they’re flexible.

33
Q

What is a fuse?

A

A tube containing a short length of wire. If the current is too high. The fuse will melt and break the circuit.

34
Q

What are circuit breakers?

A

When a circuit breaker detects a surge in current in a circuit, they break the circuit by opening a switch in live wire.

35
Q

What are two advantages and one disadvantage of circuit breakers over fuses?

A

+They cat a lot quicker

+They don’t need to be replaced every time - you just flick a switch

-They’re a lot more expensive

36
Q

How does earthing work?

A

1) If the live wire touches the metal case, the current flows down the earth wire.
2) This surge in current melts the fuse.
3) This isolated the whole appliance making it impossible to get an electric shock from it.

37
Q

What two types of fuse are generally used in plugs in the UK?

A

3A fuse for small appliances

13A fuses for highly powerful appliances

38
Q

Hat is the relationship between the cross-sectional area of a cable and the maximum safe current through it?

A

The larger the cross-sectional area, the higher the maximum safe current.

39
Q

What is an RCCB?

A

A Residual Current Circuit Breaker detects a change in current between the live an neutral wires - generally they are the same. If they become different, the RCCB opens a switch and cuts off the power.

40
Q

What are two advantages of RCCBs over fuses?

A
  • Can work for smaller current changes

* Much quicker at cutting off the electricity supply

41
Q

What is a double insulated appliance?

A

An appliance that doesn’t need an earth wire because it contains only plastic parts and no metal parts.

42
Q

What is the energy transfer when a current flows through anything with resistance?

A

Heat is produced. The greater the current or voltage, the more heat is produced.

43
Q

What happens when a charge goes through a change in potential difference?

A

Energy is transferred. Energy is supplied to the charge at the power source enough to raise it through a potential. The charge gives up Theo energy when it falls through a potential drop in components in the circuit.

44
Q

What formula links energy transferred, potential difference and charge?

A

E = V x Q

E = Energy transferred (J)

V = Potential difference (V)

Q = Charge (C)

Physics - Unit Two (6 decks)

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