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Electricity New Flashcards

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1
Q

electrical current

A

the rate of flow of electric charge

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2
Q

what is current measured in

A

amperes/amps (A)
1 amp = 1 coulomb flowing in one second

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3
Q

which way does current flow

A

positive terminal to the negative terminal of a cell

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4
Q

how to measure current

A

ammeter

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5
Q

what is charge measured in

A

coulombs (C)

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6
Q

equation linking current, charge and time

A

Q = I x t
Q = charge
I = current
t = time

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7
Q

voltage

A

-the energy transferred per unit charge passing between two points
-measured in volts(V)

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8
Q

what is one volt equivalent to

A

1 joule per coloumb

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9
Q

what happens when electrons flow through a cell

A

gain energy

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10
Q

how much energy do electrons gain when do flow through a cell

A

depending on the voltage of the cell, e.g. 12V mean 12Joules per coulomb

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11
Q

how to measure voltage

A

using a voltmeter

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12
Q

how must a voltmeter be set up

A

in parallel with the component being measure

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13
Q

why must voltmeters be set up in parallel

A

they have a very high resistant so it does not alter the flow of current

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14
Q

equation linking energy transferred, charge and voltage

A

E = Q x V

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15
Q

resistance

A

-the opposition of a component to the flow of electric current through it
-measured in ohms (Ω)

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16
Q

why are wires made of copper

A

-has a low electrical resistance, making it a good conductor

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17
Q

equation linking resistance, potential difference and current

A

V = I x R

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18
Q

how does the current change throughout a series circuit

A

current is the same throughout

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19
Q

how does current in a parallel circuit change

A

the current has different values at different points in the circuit, the sum of the current in the individual branches = total current before and after the branches

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20
Q

how does the current flowing into and out of a junction in a parallel circuit change

A

-it is the same as charge is conserved

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21
Q

how to find the total resistance of a series circuit

A

R = R1 + R2

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22
Q

how to find total voltage in a series circuit

A

V = V1 + V2 + V3

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23
Q

what does it mean for the resistance if the relationship between current and voltage is linear

A

-the resistance is constant

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24
Q

what does it mean if the relationship between current and voltage is non linear

A

the resistance is non linear

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25
Q

shape on non linear graphs including axes

A

-s shape(current increases at a proportionally slower rate
-current on y, voltage on x

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26
Q

examples of components with linear IV graphs

A

-fixed resistors at a constant temperature
-wires at a constant temperature

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27
Q

components with non-linear IV graphs

A

-filament lamps
-diodes
-LDRs
-thermistors

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28
Q

why does resistance increase as current through a filament lamp increase

A

-higher current causes the temperature of the filament to increase
-the higher temperature causes the atoms in the metal lattice of the filament to vibrate more
-increase in resistance as it becomes more difficult for free electrons to pass through
-since resistance opposes the current, this causes it to increase at a slower rate

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29
Q

diode

A

allows current to flow in one direction

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30
Q

forward bias

A

only allowing the current to flow in one direction

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31
Q

why do diodes only allow current to flow in one direction

A

it has a very high resistance and no current flow(reverse bias)

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32
Q

IV graph of a diode

A

flat when x <0, then curves up

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33
Q

ammeter

A

measures the current through the component

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34
Q

voltmeter

A

measures the voltage across the component

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35
Q

variable resistor

A

varies the current through the circuit

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36
Q

power source

A

to provide a source of potential difference(voltage

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37
Q

wires

A

connects the components together in a circuit

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38
Q

how can a circuit be set up to vary current to measure IV for a filament lamp or diode

A

-variable resistor to change the current flowing through the filament lamp/diode

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39
Q

dependent and independent variables for investigation of current and voltage for a filament lamp/diode

A

current is independent variable
voltage is dependent variable

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40
Q

how do variable resistors vary resistance

A

change the length of wire that makes up the circuit

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41
Q

what type of wires have higher resistance

A

-longer and thinner wires have more resistance

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42
Q

how does the resistance of a thermistor change

A

resistance of a thermistor depends on its temperature

43
Q

how does resistance of thermistor vary when temperature changed

A

as temperature increases, resistance of a thermistor decreases
-as temperature decreases, the resistance of a thermistor increases

44
Q

thermistor graph of resistance and temperature

A

Curves up(current on y voltage on x)

45
Q

how does resistance of an LDR vary

A

depends on the light intensity on it

46
Q

how does resistance of an LDR change with light intensity

A

-as light intensity increases the resistance of an LDR decreases
-as the light intensity decreases the resistance of an LDR increases

47
Q

how to show greater light intensity on an LDR when drawing circuits

A

more arrows onto the LDR

48
Q

LDR graph of resistance and light intensity

A

Inversely proportional

49
Q

LED/light emitting diodes

A

only allow current to flow through them in one direction

50
Q

power

A

the rate of energy or the amount of energy transferred per second

51
Q

equation linking power, current and voltage

A

P = I x V

52
Q

unit of power

A

watts(joules per second)

53
Q

what is a fuse

A

safety device to cut off the flow of electricity to an appliance if the current becomes too large

54
Q

what does a fuse consist of

A

glass cylinder containing thin metal wire that melts easily

55
Q

what happens if the current in a wire with a fuse becomes too large

A

-the wire heats up and melts
-causes the wire to break, breaking the circuit and stopping the current
-prevents more damage to the equipment or a fire

56
Q

how to choose the right rating of a fuse

A

slightly higher than the current needed by the appliance

57
Q

what happens if the fuse current rating is too low

A

-it will break the circuit when an acceptable current is flowing through

58
Q

what happens if the fuse current is too high

A

it will not break the circuit in enough time before damage occurs

59
Q

work done

A

energy transferred

60
Q

equation relating energy, power and time

A

E = P x T

61
Q

equation relating energy, current, voltage and time

A

E = I x V x t

62
Q

examples of electrical safety hazards

A

-damaged insulation - potential lethal shock of someone touches exposed wire
-overheating cables - too much current through a small wire leads to wire overheating; fire or melts insulation
-damp conditions - moisture in contact with live wires can conduct electricity, causing a short circuit in a device(fire) or electrocution risk

63
Q

safety features built into domestic appliance

A

-double insulation
-earthing
-fuses
-circuit breakers

64
Q

insulation

A

covering the conducting part of wire with an insulating material to improve electrical safety

65
Q

double insulation

A

-appliances have two layers of insulation; one around the wire and a non metallic case as a second layer of insulation
-no earthing required

66
Q

hazards of metal casing

A

if live wire comes into contact with the case, the case becomes electrified, electrocuting anyone who touches it

67
Q

what does earth wire do

A

additional safety wire to reduce risk of electrocution if live wire touches the metal casing

68
Q

what happens if live wire comes into contact with metal casing if appliance is earthed and fused

A

-earth wire provides low resistance path to the earth
-surge of current in the earth wire and in the live wire
-high current through fuse causes it to melt and break
-cuts off supply of electricity to the appliance

69
Q

circuit breaker

A

automatic electromagnet switch that breaks the circuit of the current exceeds a certain value

70
Q

advantage of circuit breaker

A

-does not melt and break, can be reset and used again
-works faster

71
Q

how is energy lost from resistacne

A

energy is dissipated into the surroundings by heating

72
Q

direct current

A

a steady current, constantly flowing in the same direction in a circuit, from positive to negative

73
Q

what appliances produce direct current

A

cells or batteries

74
Q

how does current travel in a dc circuit

A

in one direction from positive terminal to negative terminal

75
Q

alternating current

A

current that continuously changes its direction, going back and forth around a circuit

76
Q

what terminals does an alternating current power supply have

A

two identical terminals that change from positive to negative and back again

77
Q

what produces alternating current

A

electrical generators

78
Q

main electricity voltage

A

230V

79
Q

what type of current is mains electricity

A

alternating current

80
Q

what frequency does main electricity current alternate at

A

50Hz

81
Q

conductor

A

a material that allow charge to flow through it easily

82
Q

why are conductors able to conduct electricity

A

they are made up of positively charged metal ions and outermost electrons delocalised, so they are free to move

83
Q

insulator

A

material that has no free charges, does not allow the flow of charge through them very easily

84
Q

how can insulators conduct electricity

A

they can conduct static electricity, charge can build up on their surfaces and if touched the charge would be conducted away

85
Q

practical to investigate charging by friction

A
  1. Take a polythene rod, hold it at its centre and rub both ends with a cloth
  2. Suspend the rod, without touching the ends, from a stand using a cradle and nylon string
  3. Take an acrylic rod and rub it with another cloth
  4. Without touching the ends of the acrylic rod bring each end of the acrylic rod up to, but without touching, each end of the polythene rod (if the ends do touch, the rods will discharge and the forces will no longer be present)
  5. Record any observations of the polythene rod’s motion
  6. Repeat, changing out the acrylic rod for rods of different materials
86
Q

what will happen in the practical where two insulators are charged

A

-if materials is repelled, then the materials have the same charge
-if material is attracted, then the materials have opposite charges

87
Q

what happens if two objects have the same charge

A

the will repel each other

88
Q

what happens if two objects have opposite charges

A

they will attract

89
Q

what happens if a neutral object and a charged object are near each other

A

they will attract each other

90
Q

how to increase the force of two charged objects

A

bring them closer together

91
Q

what happens if an object loses electrons

A

it becomes positively charged

92
Q

what happens if an object gains electron

A

it becomes negatively charged

93
Q

what type of force is attraction and repulsion force an example of

A

non contact force

94
Q

static electricity

A

accumulation of charge on an object

95
Q

what happens when insulating materials are rubbed against each other

A

-they become electrically charged(charge by friction)
-negatively charged electrons are transferred from one material to the other

96
Q

why can charge remain on insulators

A

the charge cannot immediately flow away

97
Q

photocopiers

A
  1. Image of document is projected onto positively charged plate
  2. The plate loses its charge in the light areas and keeps the positive charge in the dark areas (i.e the text)
  3. A negatively charged black toner powder (the ink) is applied to the plate and sticks to the part where there is a positive charge
  4. The toner is then transferred onto a new blank sheet of white paper
  5. The paper is heated to make sure the powder sticks (hence why photocopied paper feels warm)
98
Q

bicycle sprays

A

-as drops of paints emerge from spray gun they are charged
-drops carry the same charge so they repel and spread out forming a thin spray
-metal bicycle frame has a wire attached to an electrical supply giving the frame opposite charge
-paint drops attracted to the surface of the frame, reaching difficult places

99
Q

inkjet printer

A

-droplets of ink are forced out of a fine nozzle, and are then given an electrical charge
-droplets are deflected as they pass between two metal plates. A voltage is given to the plates, one is -ve, one is +ve
-droplets are attracted to the plate of the opposite charge and are repelled from the plate with the same charge
-size and direction of the voltage across each plate changes so each droplet is deflected to hit a different place on the paper

100
Q

electrostatic precipitators

A

-smoke rises up chimney, passing through mesh of wires that is negatively charged
-ash and dust particles become negatively charged
-charged particles are attracted by and stick to metal earthed plates
-cleaner smoke is released into the atmosphere

101
Q

dangers of static electricity

A

-risk of electrocution
-risk of fire or explosion due to a spark close to a flammable gas or liquid

102
Q

sparking

A

-when large amounts of charge builds up, producing large potential difference across a gap
-if potential difference is large enough, current can travel through the air between objects, a spark

103
Q

how is fuelling vehicles dangerous

A

-fuel runs through pipes at a fast rate
-friction between fuel and pipe causes the fuel to gain charge
-this charge can cause a spark and fuel could ignite and cause an explosion

104
Q

how to prevent dangers of fuelling vehicles

A

-connect fuel tank to the Earth with a copper wire called bonding line during refuelling
-this carries charge through to the Earth which stops risk of sparks
-easier for charge to flow down bonding line than spark

Physics (14 decks)

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