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electricity Flashcards

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1
Q

what direction do electrons flow

A

from negative to positive

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2
Q

what is current

A

rate of flow of charge. made up of electrons

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3
Q

what is potential difference

A

electrical work done by a power supply per unit of charge flowing in a circuit

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4
Q

what is the relationship between current and potential difference

A

directly proportional

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5
Q

what is resistance

A

opposition to the flow of charge

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6
Q

what is the relationship between resistance and current

A

inversely proportional

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7
Q

what is a zero error

A

an issue with the set up/ measuring system of practical

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8
Q

in the required practical of resistance in a wire, why does the graph not go exactly through the origin?

A

other components in circuit have resistance so resistance is never at 0. it is also hard to get crocodile clips exactly at 0cm

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9
Q

what is an ohmic resistor

A

where resistance remains constant. this causes current to be directly proportional to potential difference

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10
Q

describe the IV graph for a fixed resistor

A

as potential difference increases, current also increases. directly proportional

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11
Q

describe the IV graph for a filament lamp

A

as potential difference increases, the current the current starts to increase. gradually current increases less and less each time because the filament in lamp gets hotter increasing resistance

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12
Q

describe and explain the IV graph for a diode

A

when the diode is connected the right way round then a large current flows as the potential difference increases. if connected the other way round, no current flows as resistance is so high

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13
Q

in a thermistor, what happens to resistance as temperature increases?

A

decreases

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14
Q

in an LDR, what happens to the resistance as light intensity increases

A

resistance decreases

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15
Q

what is direct current?

A

electrons flow in one direction

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16
Q

what is alternating current?

A

electrons flow in alternating directions

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17
Q

what type of current is the UK’s domestic mains supply?

A

alternating

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18
Q

what is the potential difference of the UK’s domestic mains?

A

230V

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19
Q

what is the frequency of the domestic mains supply and what does this mean?

A

50Hz

the number of times per second the live wire alternates between positive and negative

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20
Q

why do we get electric shocks when we touch live wire?

A

bodies have 0V of potential difference so if we touch it, there will be a large potential difference across the body so current will flow causing electric shock

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21
Q

what colour is the live wire?

A

brown

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22
Q

what colour is the neutral wire?

A

blue

23
Q

what colour is the earth wire?

A

green and yellow

24
Q

what does the earth wire do?

A
  • it is at 0V
  • safety device
  • if a fault occurs the wire carries current away safely
25
Q

what is the national grid?

A

a network of transformers and cables that connects power stations to where power is needed

26
Q

what does a step up transformer do?

A
  • increases potential difference
  • to reduce the current
  • reducing energy lost to surroundings as heat
  • increasing efficiency of cables
27
Q

why does the national grid work well below their maximum power output?

A

there is spare capacity to work with a higher demand

28
Q

what are conductors?

A

materials that allow charged particle to flow easily

29
Q

what are insulators?

A

materials that don’t allow charged particles to flow easily

30
Q

what does an electrical wire consist of?

A

copper core surrounded by plastic/rubber

31
Q

why do static charges only occur in insulators?

A

they do not allow the flow of electrons

32
Q

explain how rubbing an acetate rod with a cloth causes the rod and cloth to become charged

A
  • friction between the rod and cloth
  • causes electrons to transfer from rod to cloth
  • rod loses electrons and becomes positively charged
  • cloth gains to become negatively charged
33
Q

what conclusion can be drawn from hairs standing on end?

A

all charges on hair are the same
because they are repelling

34
Q

explain why a spark jumps between the negatively charged rod and earthed conductor?

A
  • there is a large potential difference between the two objects
  • causing electrons to move through the air
  • to the conductor to earth the charge
35
Q

when does an electrical field form?

A

forms around any object with an electrical charge

36
Q

which way do field lines point?

A

away from positive charge, towards negative charge

37
Q

what shows the strength of an electrical field?

A

the closer the lines, the stronger

38
Q

how can charge be transferred in air?

A
  • very large potential difference between two charged objects
  • creates a strong electric field between them
  • air particles become ionised
  • so charge can flow through it it
39
Q

when does static electricity build up on conductors?

A

conductor is unable to earth the charge as it does not have contact with the earth and an insulator isolates the charge

40
Q

what is sparking

A

as electrical charge builds up on an object, the potential difference between it and earth increases. if the pd is big enough, electrons will jump across the gap. eg lightning

41
Q

what equation links resistance, current and potential difference

A

V = I x R

42
Q

what equation links potential difference, current and power

A

P = V x I

43
Q

what equation links power, resistance and current?

A

P = I^2 x R

44
Q

what equation links energy transferred, charge flow and potential difference

A

E = Q x V

45
Q

static charge can cause a spark and making powder ignite, creating an explosion.

is an explosion more likely to happen when pumping very fine powders or when pumping powers that consist of much larger particles and why? (2)

A
  • very fine powders
  • because there is a greater charge build up
46
Q

how can the risk of exploding due to sparking in a pipe be reduced?

A

earth the pipes

47
Q

why would a variable resistor be used in a circuit? (1)

A

to obtain a range of potential difference values

48
Q

what material is used in the pin of a plug and why?

A

brass

because it is hard and a good conductor of electricity

49
Q

what material is used for the outer case of a plug and why?

A

plastic

good electrical insulator

50
Q

which wire inside a plug is the fuse connected to?

A

live wire

51
Q

how should multiple solar cells be connected so total resistance is as low as possible? (2)

A
  • in parallel
  • because current has more paths to take
52
Q

why do appliances not switch on when only one switch is closed?

A

there is a gap in the circuit

53
Q

what happens to the power output of the power supply in a parallel circuit when two switches are closed at the same time, after one already being closed? (3)

A
  • total resistance of the circuit decreases
  • so the current increases
  • which increases the power output

science (13 decks)

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