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electricity Flashcards

(57 cards)

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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

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23
Q

what colour is the earth wire?

Study These Flashcards
A

green and yellow

24
Q

what does the earth wire do?

Study These Flashcards
A
  • it is at 0V
  • safety device
  • if a fault occurs the wire carries current away safely
25
what is the national grid?
a network of transformers and cables that connects power stations to where power is needed
26
what does a step up transformer do?
- increases potential difference - to reduce the current - reducing energy lost to surroundings as heat - increasing efficiency of cables
27
why does the national grid work well below their maximum power output?
there is spare capacity to work with a higher demand
28
what are conductors?
materials that allow charged particle to flow easily
29
what are insulators?
materials that don’t allow charged particles to flow easily
30
what does an electrical wire consist of?
copper core surrounded by plastic/rubber
31
why do static charges only occur in insulators?
they do not allow the flow of electrons
32
explain how rubbing an acetate rod with a cloth causes the rod and cloth to become charged
- 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
what conclusion can be drawn from hairs standing on end?
all charges on hair are the same because they are repelling
34
explain why a spark jumps between the negatively charged rod and earthed conductor?
- 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
when does an electrical field form?
forms around any object with an electrical charge
36
which way do field lines point?
away from positive charge, towards negative charge
37
what shows the strength of an electrical field?
the closer the lines, the stronger
38
how can charge be transferred in air?
- 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
when does static electricity build up on conductors?
conductor is unable to earth the charge as it does not have contact with the earth and an insulator isolates the charge
40
what is sparking
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
what equation links resistance, current and potential difference
V = I x R
42
what equation links potential difference, current and power
P = V x I
43
what equation links power, resistance and current?
P = I^2 x R
44
what equation links energy transferred, charge flow and potential difference
E = Q x V
45
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)
- very fine powders - because there is a greater charge build up
46
how can the risk of exploding due to sparking in a pipe be reduced?
earth the pipes
47
why would a variable resistor be used in a circuit? (1)
to obtain a range of potential difference values
48
what material is used in the pin of a plug and why?
brass because it is hard and a good conductor of electricity
49
what material is used for the outer case of a plug and why?
plastic good electrical insulator
50
which wire inside a plug is the fuse connected to?
live wire
51
how should multiple solar cells be connected so total resistance is as low as possible? (2)
- in parallel - because current has more paths to take
52
why do appliances not switch on when only one switch is closed?
there is a gap in the circuit
53
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)
- total resistance of the circuit decreases - so the current increases - which increases the power output
54
what is direct potential difference?
polarity of the potential difference does not change
55
student becomes negatively charged due to friction between socks and carpet explain why friction caused student to become charged (2)
- transfer of electrons - FROM the carpet TO the student
56
negatively charged student touches a metal tap and receives an electric shock. explain why (3)
- there is a potential difference between the student and the tap - which causes electrons to transfer from the student to the tap - which earths the charge
57
why does a student rubbing their socks on a carpet with thin copper wires decrease their risk of getting an electric shock? (2)
- copper has low resistance/ copper is a conductor - so lower build up of charge on student

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