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Physics > 2b.1 - Electricity in the Home > Flashcards

2b.1 - Electricity in the Home Flashcards

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1
Q

What voltage is the UK mains supply?

A

230 V

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2
Q

What type of supply is the mains?

A

AC supply

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3
Q

What does AC stand for?

A

Alternating current

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4
Q

What is an alternating current?

A

The current is constantly changing direction - from positive to negative and back

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5
Q

What is the frequency of the AC mains supply?

A

50Hz

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6
Q

What is the unit for frequency?

A

Hz

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7
Q

What does Hz mean?

A

Cycles per second

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8
Q

What type of supply is for batteries?

A

DC

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9
Q

What does DC stand for?

A

Direct current

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10
Q

What is a direct current?

A

The current always flows in the same direction

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11
Q

What does the vertical height on an AC trace show you?

A

The input voltage - potential difference

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12
Q

How do you calculate the voltage for a DC current on an oscilloscope?

A

The distance from the straight line to the centre line

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13
Q

How do you calculate frequency?

A

1 % time period

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14
Q

Name the nine examples of electrical hazards in the home

A
  • Long cables
  • Frayed cables
  • Cables in contact with something hot or wet
  • Water near sockets
  • Shoving things into sockets
  • Damaged plugs
  • Too many plugs in one socket
  • Lighting sockets without bulbs
  • Appliances without covers
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15
Q

What colour is the earth wire?

A

Yellow and green striped

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16
Q

What colour is the neutral wire?

A

Blue

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17
Q

What colour is the live wire?

A

Brown

18
Q

What is the live wire? (3)

A
  • Brown
  • Alternated current - High
  • Current flows in
19
Q

What is the neutral wire? (3)

A
  • Blue
  • Stays at 0V
  • Current flows out
20
Q

What is the earth wire? (3)

A
  • Green and yellow striped
  • For safety
  • Attached to the metal casing and carries electricity to the earth
21
Q

What wire is screwed to the pin at the top of the plug?

A

Earth

22
Q

What wire is screwed to the pin at the left of the plug?

A

Neutral

23
Q

What wires screwed to the pin at the right of the plug?

A

Live

24
Q

What are the safety features of a plug? (4)

A
  • Right wire in right pin
  • No bare wires
  • Cable grip
  • Thick cables
25
Q

What are the features of a plug? (2)

A
  • Metal parts made from copper or brass because they are good conductors
  • The case, cable grip, and cable insulation are made of rubber or plastic because good insulators and flexible
26
Q

What prevents electrical overloads?

A

Earthing and fuses

27
Q

How does the earth wire protect the appliance? (3)

A
  • If live wire touches casing
  • Too great a current flows in through the live wire
  • Current flows through the case and down the earth wire
28
Q

How does the fuse protect the appliance? (3)

A
  • Surge in current melts fuse or trips the circuit breaker
  • This cuts off the live supply and breaks the circuit
  • This isolates the appliance
29
Q

How should fuses be rated?

A

Just higher than the normal operating current

30
Q

What is a double insulated appliance? (2)

A
  • An appliance that has a plastic case and no metal parts showing
  • Doesn’t need an earth wire
31
Q

What are the advantage circuit breakers have over fuses?

A
  • A circuit breaker’s switch can be closed but you have to buy a new fuse
  • Faster as doesn’t need to wait for fuse to melt
  • Safer as detects smaller currents
32
Q

What is an disadvantage of circuit breakers over fuses?

A

Much more expensive

33
Q

Name a type of circuit breaker

A

RCCB’s

34
Q

What does RCCB stand for?

A

Residual Current Circuit Breaker

35
Q

How does and RCCB work?

A

Detects the difference in current between the live and neural wire and cuts of power quickly by opening a switch

36
Q

What do all resistors produce when a current flows through them?

A

Heat

37
Q

What is meant of an efficient appliance?

A

It wastes less energy

38
Q

A 2.5 kW kettle is on for 5 minutes. Calculate the energy transferred by the kettle in this time.
Energy transferred = Power rating x time

A

2500 x 300 = 750 000 kJ = 750 kJ

39
Q

A hair dryer is rated at 230 V, 1 kW. Find the fuse needed.

Power = Current x Potential difference

A

1000 % 230 = 4.3 A. The fuse should be higher than normal so a 5 AMP FUSE is used.

40
Q

The motor in an electrical toothbrush is attached to a 3 V battery. If a current of 0.8 A flows through the motor for 3 minutes:
a) Calculate the total charge passed
b) Calculate the energy transformed by the motor
Energy transformed = Charge x Potential difference

A

a) 0.8 x (3 x 60) = 144 C

b) 144 x 3 = 432 J

Physics (18 decks)

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