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Physics IV > Power and electrical appliances > Flashcards

Power and electrical appliances Flashcards

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1
Q

Which wire in a plug is brown?

A

live wire

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2
Q

Which wire in a plug is blue?

A

Neutral wire

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3
Q

Which wire in a plug is green and yellow?

A

Earth wire

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4
Q

Which wire in a plug is red?

A

None

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5
Q

What is the purpose of an earth wire?

A

to carry away electrical charge from the casing of an appliance to prevent it from giving electric shocks

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6
Q

Which two wires are at 0 Volts?

A

earth and neutral wires

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7
Q

What is the voltage of the live wire?

A

230 V

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8
Q

What is the function of the live wire?

A

it provides alternating potential difference from the mains supply

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9
Q

What is the function of the neutral wire?

A

it completes the circuit and carries away the current from the appliance

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10
Q

What is the core of each wire made out of?

A

Copper

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11
Q

What is AC and where is it found?

A

alternating current. The electrons oscillate inside the wire and create a zig-zag on an oscilloscope. Found in mains supply

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12
Q

What would happen if you touched the live wire?

A

you would get an electric shock

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13
Q

What is DC and where is it found?

A

direct current. Electrons move directly along the wire to their destination, creating a straight line on an oscilloscope. Supplied by cells and batteries

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14
Q

What is the frequency of the current in the UK Mains supply?

A

50 Hz

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15
Q

Why does a moving charge transfer energy?

A

The charge does work against the resistance of the circuit.

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16
Q

Kettles transfer energy in what way to which store from the mains supply?

A

Transfer electrically from mains supply, thermal store

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17
Q

Handheld fans transfer energy in what way from where to which store?

A

electrically from battery, kinetic store

18
Q

What does the total energy transferred by an appliance depend on? Give two answers.

A

Its power (the energy that is transferred per second) and how long it is on for

19
Q

Give the equation linking energy transferred, time and power.

A

Energy transferred (J)= power (W) x time (s)
E=Pt

20
Q

What does a power rating tell you?

A

The maximum amount of energy transferred between stores each second

21
Q

An appliance transfers 6000 J of energy in 30 seconds, Calculate its power.

A

200W

22
Q

Give the equation linking charge flow, voltage, and energy transferred.

A

Energy transferred (J) = charge flow (C) x potential difference (V)
E = QV

23
Q

An appliance with a higher voltage will supply more energy to the circuit per coulomb of charge. True or False?

A

True

24
Q

Give the equation linking power, current, and voltage.

A

Power (W) = Potential difference (V) x Current (A)
P=VI

25
Q

Give the equation linking power, current, and resistance.

A

P=I^2R

26
Q

Calculate the energy transferred from a 200V source as 10,000C of charge passes.

A

2,000,000J or 2MJ

27
Q

What two things is the National Grid made up of?

A

Giant network of cables and transformers that connects the power stations to the consumers

28
Q

Why do most power stations not work to their full potential?

A

to leave spare capacity to cope with high demand.

29
Q

What occasions mean that there is a high demand of electricity?

A
  • coming home from work, school
  • when its dark, cold
  • popular events : sporting final on TV
30
Q

Why is a high potential difference needed for the electricity being carried through the national grid?

A

A very high power is required, so it needs either a high voltage or high current. If the current is high, too much energy would be wasted as thermal energy before reaching its destination. It’s a lot cheaper to boost the pd up really high and help the current as low as possible.

31
Q

How high does a step-up transformer take the voltage?

A

400,000V

32
Q

How does a step up transformer work?

A
  • It has a primary coil and a secondary coil joined with an iron core.
  • Step up transformers have more turns on the secondary coil than on the primary coil, so the voltage gets increased when it passes through
  • as the pd is increase by the transformer the current is decreased.
33
Q

What devices bring the voltage back down to a safe level, and what voltage is this?

A

step down transformers, 230V

34
Q

How does a step down transformer work?

A

They have more turns on the primary could than on the secondary.
- the pd is reduced at the local consumer and the current in increased.

35
Q

How does the power in the primary coil equal the power in the secondary coil?

A

transformers are nearly 100% efficient

36
Q

What is static electricity?

A

Charges which are not free to move, e.g. in insulating materials.
This causes them to build up on one place and it often ends with a spark or a shock when they finally do move

37
Q

How does static electricity created?

A
  • Ehen insulating materials are subbed together, negatively charged electrons will be scraped off one and dumped on the other
  • this leave the one material electrically charged with a positive static charge and the other a equal negative static charge
38
Q

Name an example of static electricity between 2 materials

A

Polythene and acetate rods
Acetate:
- loses electrons
- becomes positive
Andrew TATE lost followers/ lost electrons
Polythene:
- gains electrons
- become negative

39
Q

What happens to the potential difference between the object and the earth when electric charge builds up on a object?

A

The pd increase .
The earth is a 0V

40
Q

What happens if the potential difference gets large enough?

A

The electrons can jump across the gap between the charged object and the earth - this is a spark
- they can also jump to any earthed conductor that is nearby - which is why you can get static shocks getting out the car
- a charge builds up on the car’s metal frame and when you touch it the charge travels through you to the earth.

Physics IV (16 decks)

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