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Physics Revision > P4 - Supplying Electricity > Flashcards

P4 - Supplying Electricity Flashcards

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1
Q

power equation

A

current (squared) x resistance

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2
Q

charge flow equation

A

current x time

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3
Q

energy transferred equation

A

charge flow x potential difference

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4
Q

power equation

A

energy transferred/time

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5
Q

why is the current provided by a cell called direct current (d.c.)

A

only flows in one direction

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6
Q

what is an alternating current (a.c.)

A

current that repeatedly reverses direction

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7
Q

what kind of current is supplied by mains electricity

A

alternating current

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8
Q

what is the frequency and voltage of mains electricity

A

50Hz, 230V

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9
Q

what colours are the live, neutral, and earth wires in a three-core cable

A

live=brown, neutral=blue, earth=green and yellow stripes

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10
Q

what is the function of the live wire in a three core cable

A

carries the alternating potential difference from the supply

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11
Q

what is the function of the neutral wire in a three core cable

A

completes the circuit

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12
Q

what is the function of the earth wire in a three core cable

A

safety wire to stop the appliance becoming live

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13
Q

when is there a current in the earth wire

A

when there is a fault

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14
Q

why is the live wire dangerous

A

provides a large p.d. that would cause a large current to flow through a person if they touched it

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15
Q

what is the national grid

A

nationwide network of cables and transformers thta link power stations to customers

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16
Q

what are step-up transformers used for in the national grid

A

increase yhe p.d. from the power station to the transmission cables

17
Q

what are step-down transformers used for in the national grid

A

decrease the p.d. from the transmission cables to the mains supply in building so that it is safe to use

18
Q

what are the units for power, current, potential difference and resistance

A

watts, amps, volts and ohms

19
Q

what two things does energy transfer to an appliance depend on

A

power of appliance, time it is switched on for

20
Q

how does having a large potential difference in the transmission cables help to make the nation grid an efficient way to transfer energy

A

large p.d. means a small current is needed to transfer the same amount of power, small current in the transmission cables means less electrical power is wasted due to heating

Physics Revision (4 decks)

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