P2/Electricity Flashcards

1
Q

describe resistance in a thermistor?

A

as temperature increases resistance decreases

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2
Q

where might a thermistor be used?

A

central heating system

oven

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3
Q

describe resistance in an LDR?

A

as light intensity increases resistance decreases

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4
Q

where might an LDR be used?

A

security lighting

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5
Q

describe current in a series circuit

A

it is the same current all the way round

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6
Q

describe potential difference in a series circuit

A

the total potential difference of the power supply is shared between the components

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7
Q

describe total resistance in a series circuit

A

the total resistance of the two components is the sum of the resistance of each component

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8
Q

what is the unit for resistance?

A

Ohm

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9
Q

what is the unit for potential difference?

A

volts

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10
Q

what is the unit for current?

A

amps

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11
Q

describe current in a parallel circuit

A

the total current through the whole circuit is the sum of the currents through the separate components

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12
Q

describe potential difference in a parallel circuit

A

it is the same across each component

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13
Q

describe total resistance in a parallel circuit

A

the total resistance of two resistors is less than the resistance of the separate components

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14
Q

what is the frequency of the UK mains supply?

A

50 Hertz

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15
Q

what is the potential difference of the UK mains supply?

A

230 volts

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16
Q

mains electricity is an a.c supply.

what does this mean?

A

current constant;y changes direction

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17
Q

what does d.c mean?

A

current flows in only one direction

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18
Q

what is needed for electrical charge to flow?

A

a potential difference

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19
Q

what is electric current?

A

a flow of charge

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20
Q

what determines the size of an electrical current?

A

the rate of flow of electrical charge

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21
Q

describe the current in a series circuit

A

it is the same all the way around

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22
Q

what does current through a component depend upon?

A

the resistance of the component and the potential difference across it

23
Q

how does resistance affect current?

A

the higher the resistance the lower the current

24
Q

describe the current through an ohmic conductor

A

current is directly proportional to the potential difference

25
describe the resistance of an ohmic conductor
resistance remains constant
26
describe the resistance of a filament lamp
the resistance of a filament lamp increases as the temperature of the filament increases
27
describe current flow through a diode
current flows in one direction
28
describe resistance of a diode
very high resistance in one direction
29
what colour is the live wire?
brown
30
what colour is the neutral wire?
blue
31
what colour is the earth wire?
green and yellow stripes
32
what is the function of the live wire?
it carries the alternating potential difference
33
what is the function of the neutral wire?
completes the circuit
34
what is the function of the earth wire?
it is a safety wire to stop the appliance becoming live
35
what is the potential difference between the live wire and the earth?
230v
36
when would the earth wire carry a current?
only if there is a fault with the appliance
37
how do electric shocks occur?
when a person makes a connection between the live wire (230v) and the earth (0v)
38
what is the unit for power?
watt
39
what determines the energy an appliance transfers?
its power rating and the length of time it is switched on for
40
in an electrical circuit- work is done when...
charge flows in a circuit
41
what is the national grid?
a system of cables and transformers linking power station to the cables
42
what do step up transformers do?
increase potential difference from the power station to the cables
43
what do step down transformers do?
decrease potential difference
44
why do we use transformers in the national grid?
to reduce energy loss during transmission by using a high potential difference and low current
45
how do objects become charged?
by rubbing two insulators together
46
why do objects become charged?
because they gain or lose electrons
47
what is the charge of a material that gains electrons?
negative
48
what is the charge of a material that loses electrons
positive
49
two objects that carry the same charge will ....... each other
repel
50
two objects that carry opposite charge will ....... each other
attract
51
is electrostatic force a contact or non-contact force?
non-contact
52
what can be found around a charged object?
an electric field
53
where is the field strongest?
nearest the charged object