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Physics Nat 5 > topic 2 - electricity: energy transfers > Flashcards

topic 2 - electricity: energy transfers Flashcards

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1
Q

What is the equation which links power, potential difference and current?

A

power = potential difference x current

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2
Q

What is the symbol for power?

A

P

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3
Q

What is the symbol for potential difference?

A

V

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4
Q

What is the symbol for current?

A

I

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5
Q

What is the equation which links power, current and resistance?

A

power = (current)2 x resistance

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6
Q

What is the symbol for resistance?

A

R

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7
Q

What is the power of an appliance?

A

The amount of energy that it transfers per second.

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8
Q

What are the units for power?

A

watts (W)

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9
Q

What are the units for potential difference?

A

volts (V)

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10
Q

What are the units for current?

A

amps (A)

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11
Q

What are the units for resistance?

A

ohms (Ω)

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12
Q

What two factors does the total energy transferred by an appliance depend on?

A

How long the appliance is on for and it’s power.

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13
Q

Will a circuit with high current and potential difference have a high or low power?

A

High.

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14
Q

What are everyday electrical appliances designed to bring about?

A

Energy transfers.

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15
Q

How does a kettle transfer energy from ac mains to the heating device?

A

Kettles transfer energy electrically from the mains ac supply to the thermal energy store of the heating element inside the kettle.

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16
Q

How is energy transferred from the battery of a handheld fan to its electric motor?

A

Energy is transferred electrically from the battery of a handheld fan to the kinetic energy store of the fan’s motor.

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17
Q

What has to flow in a circuit to allow work to be done?

A

Charge.

18
Q

What is the equation that links energy transferred, power and time (equation for energy transferred by electrical work)?

A

energy transferred = power x time

19
Q

What is the equation that links energy transferred, charge flow and potential difference?

A

energy transferred = charge flow x potential difference

20
Q

What is the symbol for energy transferred?

A

E

21
Q

What is the symbol for power?

A

P

22
Q

What is the symbol for time?

A

t

23
Q

What is the symbol for charge flow?

A

Q

24
Q

What is the symbol for potential difference?

A

V

25
Q

What are the units for energy transferred?

A

joules (J)

26
Q

What are the units for power?

A

watts (W)

27
Q

What are the units for time?

A

seconds (s)

28
Q

What are the units for charge flow?

A

coulombs (C)

29
Q

What are the units for potential difference?

A

volts (V)

30
Q

What is potential difference?

A

Energy transferred per charge passed.

31
Q

Will a battery with a higher potential difference supply more or less energy to the circuit per coulomb of charge?

A

More energy.

32
Q

What is the power rating of an appliance?

A

The maximum safe power that an appliance can operate at.

33
Q

The power rating of an appliance tells you the _______ amount of ______ transferred between stores ___ ______ when the appliance is on.

A

maximum, energy, per second

34
Q

Why do power ratings help customers choose between models of an appliance?

A

The lower the power rating, the less electricity an appliance uses in a given time and so the cheaper it is to run.

35
Q

Why does a high power rating not necessarily mean that an appliance transfers more energy usefully?

A

An appliance may be more powerful than another, but less efficient, meaning that it might transfer the same amount of energy (or less) to the useful stores.

36
Q

What is the National Grid?

A

A system of cables and transformers linking power stations to consumers.

37
Q

What type of power is transferred from power stations to consumers using the National Grid?

A

Electrical power.

38
Q

Why do power stations often run well below their maximum output?

A

So there is spare capacity to cope with an unexpected spike in demand.

39
Q

Why is the National Grid system an efficient way to transfer energy?

A

It uses a high pd (400,000 V) and a low current which is cheaper and decreases the energy lost by heatint the wires and the surroundings.

40
Q

What is the purpose of step-up transformers in the National Grid?

A

Increase the potential difference from the power station to the transmission cables.

41
Q

What is the purpose of a step-down transformer in the National Grid?

A

Decrease, to a much lower value, the potential difference to make the power suitable for domestic use.

Physics Nat 5 (30 decks)

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