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year 10 mock exam revision > physics topic 2 - electricity > Flashcards

physics topic 2 - electricity Flashcards

1
Q

what is electric current?

A

the flow of electric charge

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2
Q

how will current only flow around a complete circuit?

A

if there is a potential difference

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3
Q

what is the unit of current?

A

amperes, a

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4
Q

what is potential difference and what does it do?

A

voltage, its the driving force that pushes around the charge

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5
Q

what is the unit for potential difference?

A

volts, v

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6
Q

what is resistance?

A

anything in a circuit which slows the flow of charge down

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7
Q

what is the unit of resistance?

A

ohms

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8
Q

what does the current flowing through a component depend on?

A

the potential difference across it and the resistance of the component

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9
Q

the greater the resistance across a component=

A

the smaller the current that flows through it

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10
Q

when current flows past a point in a circuit for a length of time then the charge that has passed is given in what formula ?

A

I(current)=Q(charge)/ T (time)

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11
Q

what is charge measured in?

A

coulombs

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12
Q

what is time measured in?

A

seconds

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13
Q

what passes through a circuit more when a bigger current flows?

A

more charge

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14
Q

what does the symbol for a fuse look like?

A

a rectangle with a line going all the way through it

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15
Q

what does the symbol for an LED look like?

A

a play button with two right upward diagonal arrows

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16
Q

what does the symbol for a resistor look like?

A

a rectangle with no line going all the way through it

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17
Q

what does the symbol for a variable resistor look like?

A

a rectangle with an upward right facing arrow going diagonally

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18
Q

what does the symbol for a diode look like?

A

a play button

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19
Q

what does the symbol for an LDR look like?

A

a circle with a rectangle in it with two diagonal arrows coming down on it from the left

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20
Q

what does the symbol for a thermistor look like?

A

rectangle with a line that goes through it diagonally (it starts straight underneath)

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21
Q

what is the equation for resistance?

A

R=V/I

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22
Q

what is the resistance of an ohmic conductor like?

A

it is constant and the current flowing the ohmic conductor is directly proportional to the potential difference across it

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23
Q

in what components does resistance change?

A

filament lamp, diode

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24
Q

what happens when an electrical charge flows through a filament lamp?

A

it transfers some thermal energy to the lamp which heats up

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25
Q

with the filament lamp what increases with the current ?

A

resistance

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26
Q

what does resistance depend on with diodes?

A

the direction of the current

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27
Q

what happens with diodes?

A

they will happily let current flow in one direction but if its reversed the resistance is very high

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28
Q

what does the term IV characteristics refer to?

A

a graph which shows the current flowing through a component as the potential difference across it increases

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29
Q

what do linear (ohmic) components have?

A

have an IV characteristic that’s a straight line

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30
Q

what do non linear (non ohmic) components have?

A

have a curved IV characteristic

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31
Q

how do you set up an experiment to find a components IV characteristic?

A

set up a test circuit and use a variable resistor to alter the pd and current across the component. take several reading then swap the wires so the direction is reversed and repeat steps

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32
Q

what is the IV graph for an ohmic conductor like?

A

current directly proportional to p.d., so you get a straight line

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33
Q

what is the IV graph like for a filament lamp?

A

when the current makes the temperature of the filament increase, the resistance increases. less current can flow through as the resistance increases so the graph gets shallower

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34
Q

what is the IV graph for a diode like?

A

current only flows through a diode in one direction so the diode has high resistance in the reverse direction

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35
Q

what is an LDR?

A

a resistor that is dependant on the intensity of light

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36
Q

in bright light what happens to an LDR?

A

resistance falls

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37
Q

in darkness what happens to an LDR?

A

the resistance goes up

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38
Q

give an example of an LDR component?

A

street lights/ burglar detectors

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39
Q

what does the graph for an LDR look like?

A

as the light intensity gets higher the resistance gets lower

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40
Q

what is a thermistor?

A

a temperature dependant resistor

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41
Q

what’s a thermistor like in hot conditions?

A

the resistance drops

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42
Q

what’s a thermistor like in cool conditions?

A

the resistance goes up

43
Q

give an example of a thermistor component?

A

electronic thermostats

44
Q

what does the graph for a thermistor look like?

A

as the temperature increases the resistance decreases

45
Q

what are sensing circuits used for?

A

to turn on or increase the power of components on the conditions that they are in

46
Q

how is the thermistor used in the circuit of a fan?

A

as the heat increases the resistance in the thermistor drops and the fan can go faster to cool it down

47
Q

how can you connect the LDR across a variable resistor instead of a fixed one?

A

if you connect a bulb in parallel to an LDR , the p.d.across both the LDR and the bulb will be high when its dark so the bulb will get brighter as the room gets darker

48
Q

in series circuits, what happens with the p.d. of the cells if there is more than one?

A

they add up

49
Q

what happens to the p.d. in a series circuit?

A

the p.d. of all the components adds up to the p.d. of the power supply

50
Q

what is the current like in a series circuit?

A

current in the same everywhere

51
Q

whats the size of the current determined by?

A

the total p.d. of the cells and the resistance of the circuit ( I = V/R)

52
Q

what happens to resistance in a series circuit?

A

the total resistance of two components is just the sum of their resistance

53
Q

what is the p.d. like across a parallel circuit ?

A

every component has the same p.d. and get the full source p.d.

54
Q

what is current like across a parallel circuit?

A

the total current is the sum of the current of each component

55
Q

what happens to resistance in a parallel circuit ?

A

if you have two resistors in parallel, their total resistance is less than the resistance of the smallest of the two resistors

56
Q

how can you investigate the resistance by adding more resistors in series?

A

keep adding resistors in series measuring the pd. and current as you go

57
Q

how can you investigate the resistance by adding more resistors in parallel?

A

build a parallel circuit and calculate the current and resistance. after add a resistor in parallel and measure the current going through the whole circuit and use this and the o.d. to calculate the resistance across the whole circuit

58
Q

in series what, should the graph look like for the investigation?

A

as the number of identical resistors increases, so does the resistance

59
Q

in parallel what should the graph look like for the investigation?

A

as you add the number of identical resistors, the overall resistance decreases

60
Q

what happens in ac supplies?

A

the current constantly changes direction

61
Q

the uk mains supply is ac, how much is it at?

A

230v

62
Q

what is the frequency of the ac mains supply ?

A

50 cycles per second or 50Hz

63
Q

what is dc (direct current)?

A

supplied by cells and batteries

64
Q

what direction does direct current go in?

A

it always flows in the same direction

65
Q

what colour is neutral wire?

A

blue( around 0v)

66
Q

what colour is the live wire?

A

brown ( provides the 230v from the mains supply)

67
Q

what colour is the earth wire?

A

green and yellow (0v and protects the wiring)

68
Q

what wire gives you an electric shock as current flows through you?

A

live wire

69
Q

energy transferred depends on what?

A

the power

70
Q

the total energy transferred by an appliance depends on what?

A

how long the appliance is on for and its power

71
Q

what is the equation for energy transferred?

A

energy transferred = power x time

72
Q

what are appliances given so that you can see the maximum power it can work at before it becomes dangerous?

A

a power rating

73
Q

what does the power rating tell you?

A

the maximum amount of energy transferred

74
Q

how does the power rating help customers?

A

it helps them choose between models because the lower the power rating the cheaper it is to run

75
Q

an appliance may be more powerful but might not be what?

A

efficient

76
Q

what is potential difference?

A

energy transferred per charge passed

77
Q

when an electrical charge goes through a change in potential difference, what happens ?

A

energy is transferred

78
Q

what is the formula for energy transferred ?

A

energy transferred = charge x voltage

79
Q

how can you calculate the power of an appliance?

A

power= p.d. x current

80
Q

how do you find the power if you don’t know the p.d.?

A

p= I squared x r

81
Q

what is the national grid?

A

a giant system of cables and transformers that covers the UK to connect power stations to consumers

82
Q

what does the national grid do?

A

transfers electrical power from power stations anywhere on the grid to anywhere else on the grid where its needed

83
Q

power stations have to use enough electricity because?

A

the demand (usage ) for electricity changes throughout the day therefore enough has to be supplied

84
Q

when does demand increase for electricity?

A

when people : get up, come home from school/ work , when it starts to get dark/cold and major sports events

85
Q

power stations often run well below what?

A

their maximum power output , so there’s spare capacity to cope with the high demand

86
Q

what is kept at standby in case the demand isn’t enough?

A

lots of smaller power stations

87
Q

to transmit a huge amount of power what do you need?

A

either a high potential difference or a high current

88
Q

what is the problem with a high current?

A

you lose loads of energy as the wires heat up and the energy is transferred to the thermal energy store of the surroundings

89
Q

its must cheaper to boost up what?

A

to boost up the p.d. really high and keep the current low

90
Q

what is the p.d. boosted up to in the national grid?

A

400,000v

91
Q

how is the national grid efficient ?

A

the pd increases decreasing the current which decreases energy lost by heating the wires and the surroundings

92
Q

how does the potential difference change in the national grid?

A

through transformers and pylons with huge insulators

93
Q

what do step up and step down transformers do?

A

step up transformers make the p.d. bigger to go into the pylons and step down transformers bring it back down to safe, stable levels

94
Q

what is static electricity caused by?

A

friction

95
Q

what happens when certain insulating materials rub together?

A

negatively charged electrons will be scraped off one and dumped on the other

96
Q

what does it leave when electrons rub off onto other materials in static electricity?

A

it leaves materials electrically charged, with a positive static charge on one and an equal negative static charge on the other

97
Q

what never moves in static electricity?

A

positive charges

98
Q

a positive static charge is always caused by what?

A

electrons moving away elsewhere

99
Q

as electric charge builds up on an object what happens to the p.d.?

A

the potential difference between the object and the earth increases

100
Q

if the potential difference in an object gets large enough what happens?

A

electrons can jump across the gap between the charged object and the earth- this is a spark

101
Q

how can you get static shocks getting out a car?

A

electrons can jump to any earthed conductor that is nearby. a charge builds up on the metal doorframe an when you touch it the charge travels through you to earth

102
Q

opposite charges do what?

A

attract

103
Q

when charges get further apart what happens to the forces?

A

they get weaker

104
Q

what opposite force is there between opposite charges?

A

electrostatic attraction

year 10 mock exam revision (26 decks)

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