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Electricity Flashcards

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1
Q

what is needed for charge to flow

A

circuit must be closed
must be a source of potential difference (battery/cell)

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2
Q

what is current

A

the flow of charge

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3
Q

what is the current like in a single , closed loop

A

same value at any point

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4
Q

what does the current in a component depend on

A

resistance of the component and potential difference across the component

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5
Q

what happens when there is a greater resistance in a component

A

smaller the current for a given potential difference

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6
Q

what is ohms law

A

the current passing through a component is directly proportional to the potential difference across it ,provided the temperature is constant

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7
Q

what happens to the graph is the resistance of the components is not constant and changes with the current in the component

A

non linear

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8
Q

how does resistance change with current

A

as current increases electrons have more energy
when electrons flow through a resistor they collide with atoms in the resistor
this transfers energy to the atoms causing them to vibrate more
this makes it harder for electrons t flow through the resistor
resistance increases and current decreases

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9
Q

how does resistance change with temperature in normal wires

A

as temperature increases atoms have more energy
when atoms flow through the resistor they collide with others
transferring mor energy and making them vibrate more
so it is difficult for flow through a resistor
resistance increases

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10
Q

how does temperature effect resistance in a thermistor

A

in hotter temperatures resistance is lower
often used in temperature detectors/thermostats

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11
Q

how does length affect resistance

A

greater the length the more resistance and lower the current
electrons have to make their way through more resistor atoms so harder than using short wire

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12
Q

how does light affect resistance (with an LDR)

A

greater the light intensity , lower the resistance
resistance is greatest when dark
used in automatic night lights

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13
Q

how does voltage affect resistance (in diodes)

A

diode allows current to flow freely in one direction
in the opposite direction it has a high resistance so no current can flow

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14
Q

what is resistance

A

a measure of how much a material tries to stop current

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15
Q

how does diameter affect resistance

A

increasing diameter decreases resistance

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16
Q

how does conductivity affect resistance

A

increasing conductivity decreases resistance

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17
Q

what are series circuits

A

closed circuit
current follows a single path
current is the same everywhere
total resistance = r1 + r2

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18
Q

what is a parallel circuit

A

branched circuits
current splits into multiple paths
total current into a junction= total current in each of the branches
the potential difference is the same across each branch

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19
Q

what is the total resistance for two resistors like in parallel

A

less than the resistance of the smaller resistor

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20
Q

how are the components connected in series circuits

A

end to end

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21
Q

how are components connected in parallel circuits

A

separately to the power supply

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22
Q

how does the current flow through components in series

A

all the current flows through all the components

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23
Q

how does current flow through parallel

A

flows through each component seperately

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24
Q

how is potential difference shared across a series circuit

A

shared across whole circuit
pd of power supply=sum of pd across each component

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25
Q

how is current shared through series

A

same through all parts of the circuit
current at one point =current at any other point

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26
Q

how is total resistance shared through series

A

sum of resistance in each component
resistance of two components is bigger than just one of them because the charge has to push through both of them when flowing round the circuit

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27
Q

how is potential difference shared through parallel circuits

A

same across all branches
pd of power supply=pd of each branch
charge can only pass through any one branch

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28
Q

how is current shared between parallel

A

shared between each of the branches
current through source = sum of current through each branch

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29
Q

what is the resistance across parallel

A

total is less than the branch with the smallest resistance
two resistors in parallel will have a smaller overall resistance than just one
charge has more than one branch to take so only some charge will flow along each branch

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30
Q

what does an IV graph show

A

how the current passing through a component changes with potential difference

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31
Q

what are the components of an IV graph

A

fixed resistor
filament bulb
diode

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32
Q

what kind of supply is mains electricity

A

AC supply

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33
Q

what is the frequency of mains electricity in the uk

A

50hz

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34
Q

what is the voltage of mains electricity in the uk

A

230 V

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35
Q

what is ac

A

alternating current , comes from mains
current continuously varies from positive to negative (charge changes direction)

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36
Q

what is dc

A

direct current , movement in one direction only
cells and batteries supply direct current

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37
Q

what is peak voltage

A

the maximum height of wave (in a vertical direction) from the zero line
measured in volts

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38
Q

what is time period of waves

A

the time for one complete wave to pass, measured in seconds

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39
Q

what is frequency

A

the number of complete waves passing a point per second, measured in hertz

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40
Q

what is the frequency equation

A

1/ time period or f=1/t

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41
Q

how do you get an ac supply

A

needs plugging in from mains , produced by generators

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42
Q

what colour is live wire

A

brown

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43
Q

what voltage is live wire

A

±325V

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44
Q

what is the function of a live wire

A

provides the large alternating pd between it and the neutral wire so an alternating current is produced to power the appliance

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45
Q

what colour is a neutral wire

A

blue

46
Q

what is the voltage of a neutral wire

A

close to 0V

47
Q

what is the function of a neutral wire

A

provides a potential difference close to 0V for the live wire to produce a large alternating pd between the two wires

48
Q

what is the colour of an earth wire

A

yellow/green

49
Q

what is the voltage of an earth wire

A

0V

50
Q

what is the function of an earth wire

A

connected to metal cases of an appliance and stops it becoming live if the live wire touches the case. this stops the risk of electric shock to the user

51
Q

how would you get an electric shock from live wires

A

if it touches the metal casing of the appliance it will become live
you get a serious electric shock if you touch it as current flows through you to the ground

52
Q

why is three pin plugs case made of stiff plastic

A

a poor conductor(insulator) and strong so hard to damage

53
Q

why are wires inside of a plug made if copper

A

a good conductor and flexible

54
Q

why are pins in a plug made of brass

A

a good conductor, very strong and doesn’t rust

55
Q

why are the wires covered in rubber in plugs

A

a poor conductor (insulator) and flexible

56
Q

which appliances need an earth wire

A

only metal appliances
there is a risk of electrocution to the user if there is a fault

57
Q

which cables do plastic appliances need

A

two core cables

58
Q

how are plastic appliances double insulated

A

the case is made from plastic and copper wires are insulated with rubber

59
Q

what is a fuse

A

a safety measure to stop appliances overheating and causing a fire.
they protect an appliance
connected directly to the live wire inside the plug

60
Q

what is power

A

energy transferred per second.
directly proportional to current and voltage

61
Q

what is power loss proportional to

A

resistance , the square of the current

62
Q

where is energy transferred from and to to be useful energy in devices

A

transferred from chemical potential in batteries to electrical energy in wires to any form of useful energy in the devices they power

63
Q

which calculation is for electrical power of an appliance

A

power = current x potential difference or p = i x v

64
Q

what is resistance and its heating effect

A

when an electric current passes through a conductor, resistance causes the conductor to heat up
as the resistor heats up it transfers energy to the surroundings by heating therefore acting as a heater

65
Q

what is the power equation by current and resistance

A

p = I ˆ2 x R

66
Q

what is the national grid

A

a system of cables and transformers linking power stations to consumers across the uk

67
Q

how is electricity transferred to uk homes

A

electricity is generated in a power station and transported around the uk by the national grid

68
Q

what do transformers do

A

change the voltage and current.
transmitting electricity at high voltage reduces power loss , making the system more efficient

69
Q

what is stepping up

A

increasing the voltage and decreasing the current so a very small current flows through the wires. this reduces heat loss and makes it a more efficient process

70
Q

what is stepping down

A

decreasing the voltage and increasing the current. our homes and offices operate on a voltage of 230v so the voltage needs to be stepped down to make it safe for use

71
Q

what do step up transformers do

A

increase. the pd from the power station to the national grid
so as the power is constant , current decreases so less energy is lost

72
Q

what do step down transformers do

A

decrease the pd
from the national grid to consumers
for consumer safety

73
Q

what is the amount of energy transferred affected by

A

amount of charge that passes through it each second
potential difference across the resistor

74
Q

what is the energy in a circuit equation

A

energy = charge x potential difference

75
Q

what causes objects to become charged

A

if friction causes electrons to be transferred

76
Q

what happens when a cloth becomes negatively charged

A

electrons move from the cloth to the insulator so it becomes negatively charged

77
Q

which particles are free to move in static electricity

A

electrons

78
Q

what happens if potential difference exists between the two points

A

negatively charged electrons will move towards the positive side, this is a current flow

79
Q

what happens if two conductors are rubbed

A

electrons will flow in / out of them cancelling out any effect, so they stay neutral

80
Q

when does sparking occur

A

when charge builds up, and objects are close but not touching
spark is when charge jumps through the air from highly negative object to highly positive object to balance the charges

81
Q

what do the charged objects experience

A

a force- electrostatic force of attraction or repulsion

82
Q

what are electric fields

A

fields for charges

83
Q

which direction do electric fields go in

A

the direction the proton would move = away from positive charges, towards negative charges

84
Q

what happens if a charged object enters an electric field

A

experiences a force

85
Q

how can objects become charged?

A

if friction causes electrons to be transferred

86
Q

what happens if a proton moves into a positive electric field

A

it would repel

87
Q

what happens if an electron moves into a positive electric field

A

it would attract

88
Q

what happens if there is a potential difference between two points

A

negatively charged electrons will move towards the positive side (current flow)

89
Q

what is a cell

A

a source of energy

90
Q

what does an LED do?

A

emits light when a current is passed through it

91
Q

what does a variable resistor do

A

allows the current to be varied

92
Q

what is a cell necessary for

A

push electrons around a complete circuit
a battery consists of two or more cells

93
Q

what does a diode do

A

allows current through in one direction only

94
Q

what does a voltmeter do

A

measure potential difference

95
Q

what does a switch do

A

enables the current in a circuit to be switched on or off

96
Q

what does an indicator do

A

emit light as a signal when a current passes through it or a light source such as a lamp

97
Q

what does a fuse do

A

melt and therefore break the circuit if the current through it is greater than a certain amount

98
Q

what does a fixed resistor do

A

limits the current in a circuit

99
Q

what does an ammeter do

A

measure electric current

100
Q

what is an electrical current

A

the rate of flow of charge (how much charge flows through a point in the circuit in one second)

101
Q

what is the charge on an electron

A

1.6 x 10^-19

102
Q

no of electrons

A

charge / charge of electrons

103
Q

what is potential difference

A

the work done (energy transferred, J) per coulomb charge that passes between the points

104
Q

what does a bigger potential difference mean

A

a bigger push for electrons = more current flowing

105
Q

what is potential difference measured in and with

A

volts, voltmeter

106
Q

what is the voltage equation

A

work done / charge

107
Q

what is the LDRs resistance affected by

A

light intensity

108
Q

what is an LDR useful for

A

where light levels drip below a certain value so a light can be triggered to turn on
eg street lights

109
Q

what is the LDR rule

A

Brightness Increases Resistance Decreases
BIRD

110
Q

what is resistance affected by in a thermistor

A

temperature

111
Q

what are thermistors used in circuits for

A

to regulate temperatures
eg gas ovens, thermostats

112
Q

what is the rule for thermistors

A

TURD
Temperature Up Resistance Down

Physics (19 decks)

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