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Physics > P5 Electricity > Flashcards

P5 Electricity Flashcards

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1
Q

What is alternating current

A

An electric current in a circuit that repeatedly reverses its direction

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2
Q

What is direct current

A

An electric current in a circuit that is in one direction only

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3
Q

What is an earth wire

A

The wire in a mains cable used to connect the metal case of an appliance to earth

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4
Q

What is a fuse

A

A fuse contains a thin wire that melts and cuts the current off if too much current passes through it

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5
Q

What is a live wire

A

The mains wire that has a voltage that alternates in voltage

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6
Q

What is the alternating voltage of live wires in Europe

A

+325V and -325V

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7
Q

What is a neutral wire

A

The wire of a mains circuit that is earthed at the local substation, so its potential is close to zero

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8
Q

What is an oscilloscope

A

A device used to display the shape of an electrical wave

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9
Q

What is a plug

A

A plug has an insulated case and is used to connect the cable from an appliance to a socket

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10
Q

What is a step-down transformer

A

An electrical device used to step-down the size of an alternating potential difference

National grid => consumers

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11
Q

What is a step-up transformer

A

An electrical device used to step-up the size of an alternating potential difference

Power station => national grid

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12
Q

What produces direct current

A

Cells

Batteries

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13
Q

What produces alternating current

A

Generators

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14
Q

What uses direct current

A

Electronic circuits

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15
Q

What uses alternating current

A

Mains electricity

Motors

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16
Q

Can direct current be efficiently transferred over long distances

A

No

17
Q

Can alternating current be efficiently transferred over long distances

A

Yes

18
Q

How are hertz calculated

A

cycles / second

19
Q

What is the alternating p.d produced by power stations

A

~25,000V

20
Q

What is the frequency of mains electricity in the UK

A

~50Hz

21
Q

What is the voltage of mains electricity in the UK

A

230V

22
Q

What changes AC to DC

A

A rectifier
E.g. a diode

These components only allow current to flow in one direction

23
Q

How is hertz calculated using cycle time

A

Hz(ac) = 1 / time(cycle)

24
Q

How is peak wattage calculated

A

W(peak) = 2W(stated)

bc W(stated) = W(average)

25
Q

How is P(av) calculated

A

(current(max) * voltage(max)) / 2 OR wattage(max) / 2

Physics (8 decks)

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