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GCSE - Physics > P5 - electricity in the home > Flashcards

P5 - electricity in the home Flashcards

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1
Q

what is direct current (DC)

A

current that only goes in one direction

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2
Q

what is alternating current (AC)

A

a current that repeatedly reverses it’s direction

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3
Q

what is an alternating currents frequency

A

the number of cycles it passes through each second

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4
Q

what is the mains frequency in the UK

A

50Hz

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5
Q

compare the potential difference in an AC and DC circuit

A

AC - PD repeatedly reverses it’s direction
DC - PD does not change direction

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6
Q

where is the neutral wire earthed

A

the local electricity substation

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7
Q

why is the live wire dangerous

A

it’s potential repeatedly changes from + to - in every cycle

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8
Q

what voltage does the live wire reach in uk homes

A

325 V

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9
Q

what are step up transformers used for

A

to transfer electricity to the national grid

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10
Q

what do step up transformers do

A

increase size of the alternating current from around 25000 V to 132000 V

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11
Q

what are step down transformers used for

A

to supply electricity from the national grid to consumers

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12
Q

how much power are factories provided witth

A

100kV or 33kV

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13
Q

how much power are home supplied with

A

230V

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14
Q

how is the national grid efficient

A

the pd is very large, less current is needed to transfer same amount of power
power loss due to resistance heating in cables is reduced

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15
Q

what is the equation to measure frequency of an AC supply

A

frequency = 1/time taken for 1 cycle

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16
Q

what does the earth wire do

A

stops the metal case in a plug becoming live if the live wire breaks

17
Q

why are the pins in a three pin plug made of brass

A

brass is a good conductor
doesn’t rust or oxidise

18
Q

why is the case of a plug shaped a certain way

A

so the wires and pins can’t touch eachother

19
Q

where is the brown wire connected to in a plug

A

the live pin

20
Q

where is the blue wire connected to in a plug

A

the neutral pin

21
Q

where is the green and yellow striped wire connected to in a plug

A

the earth pin

22
Q

why is copper used for the wires in a plug

A

good electrical conductor
bends easily (ductile)

23
Q

why is plastic used for the cable in a plug

A

good electrical insulator
if anyone touches the cable they don’t get shocked

24
Q

what is the equation connecting power, energy, and time

A

p = e/t

25
Q

what is current in an electrical appliance

A

the charge that flows through it each second

26
Q

what is pd in an electrical appliance

A

the energy transferred to the appliance by each coulomb of charge that passes through it

27
Q

what is the equation linking power current and pd

A

p = i x v
PEE ON IVY

28
Q

what are the three fuse options domestic appliances are fitted with

A

3A
5A
13A

29
Q

what is the equation linking power, current, and resistance

A

power = current^2 x resistance

30
Q

what equation do you use to check the correct rating for a fuse

A

electrical power (watts) / potential difference (volts)

31
Q

what is the equation for charge flow

A

charge flow = current x time

32
Q

how does a resistor become hotter

A

electrons pass through resistor and collide with vibrating metal ions of resistor transferring energy to ions
ions gain kinetic energy, vibrate more
resistor becomes hotter

33
Q

how do you calculate energy in a resistor (2 options)

A

energy = charge flow x pd
energy = power x time = pd x current x time

34
Q

when charge flows around a circuit, what is the energy supplied equal to

A

the energy transferred to all the components in a circuit

35
Q

what is the equation linking power, current, and potential difference

A

power = current x pd

36
Q

what is the equation for efficiency

A

output power/input power x 100

37
Q

can the efficiency of an electrical appliance be 100% ?

A

no it’s always less than 100%

38
Q

why/how do electrical appliances waste energy

A

current in wires and components has a heating effect due to resistance of wires and components
energy is transferred by heating to surroundings

GCSE - Physics (7 decks)

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