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electricity Flashcards

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1
Q

what is electrical current?

A

the flow of charge

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2
Q

charge flow ( q ) =

A

current x time ( it )

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3
Q

what is charge flow measured in + what is its symbol?

A

coulombs

q

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4
Q

what is current measured in + what is its symbol?

A

amps

i

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5
Q

in a closed loop does the current always remain the same?

A

yes

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6
Q

potential difference ( v ) =

A

current x resistance ( ir )

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7
Q

the greater the resistance the smaller the

A

current ( for any pd )

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8
Q

what is resistance measured in + what is its symbol?

A

ohms Ω

r

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9
Q

describe the relationship between current and potential difference in an ohmic conductor

A

the current through an ohmic conductor is directly proportionate to the pd

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10
Q

on a current vs potential difference graph which is on the y-axis?

A

potential difference

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11
Q

why does a current vs potential difference graph look like it does for a filament lamp?

A
  • it has shallow ends ( high resistance ) because of the temperature increases and the bulb is bright
  • it is steep at the centre ( low resistance ) and the bulb is dim
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12
Q

what happens to the resistance of a filament bulb when the temperature increases?

A

it increases

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13
Q

what does a shallow line signify on a current vs pd graph?

A

high resistance

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14
Q

why does the current decrease when the temperature increases ( filament lamp) ?

A

if the wire is hot then the ions will vibrate and collide which makes it harder for electrons to flow through, increasing the resistance and decreasing the current

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15
Q

how is current affected by increasing resistance?

A

it decreases

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16
Q

why does a current vs potential difference graph look like it does for a diode?

A
  • charge only flows one way in a diode so that is why there are no negative values
  • when the pd increase over the threshold the diode has a steep line ( high resistance )
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17
Q

what happens to the resistance of an ldr as the temperature increases?

A

it decreases :0

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18
Q

what is ac?

A

alternating current - the direction that the electron flow in changes periodically

19
Q

what is dc?

A

direct current - electrons only flow one way, found in batteries

20
Q

what is the frequency and demand of electricity in the uk?

A

about 50Hz and 230V

21
Q

what is the role of the live wire and what is its colour?

A

brown and it carries the potential difference around the circuit ( 230V )

22
Q

what is the role of the neutral wire and what is its colour?

A

blue and it completes the circuit ( 0V )

23
Q

what is the role of the earth wire and what is its colour?

A

yellow and green and it is a safety wire to stop the appliance becoming live ( 0V unless there is a fault )

24
Q

power = ( p )

A

pd x c ( IV ) or I^2 x r ( I^2R )

25
Q

describe the current in a series circuit

A

the current is consistent/the same anywhere in the circuit / the same through any component

26
Q

describe the voltage in a series circuit

A

the voltage around the power pack is the sum of the voltage at the components, the voltage at the components is not necessarily the same

27
Q

describe the current in a parallel circuit

A

the current at the battery is the sum of the currents through the separate components

28
Q

describe the voltage in a parallel circuit

A

the voltage is consistent/the same anywhere in the circuit

29
Q

describe the resistance in a series circuit

A

the total resistance of two components is the sum of the resistance of each component. Rt = R1 + R2

30
Q

describe the resistance in a parallel circuit

A

the total resistance of two resistors is less than the resistance of the smallest individual resistor.

31
Q

define power in terms of energy transferred and time

A

power = energy transferred / time

32
Q

how can a live wire still be dangerous when a switch in the circuit is open?

A

the live wire between the wall and switch is still alternating so if someone touched that live wire they could get a shock because of the pd between the live wire and earth

33
Q

what are the peaks of our mains electricity?

A

+/- 325 V

34
Q

what is the purpose of step - up and step down transformers?

A

to increase the voltage for efficiency and then decrease it for domestic use

35
Q

why does touching a live wire result in a large current flowing through you?

A

the live wire is at a high potential
and the person is at zero
so touching the wire creates a large potential difference
so a large current flows to the earth

36
Q

what is the equation for efficiency in terms of power?

A

useful power output / total power input

37
Q

what is the purpose of a fuse?

A

an electrical component featuring a thin wire which melts if the current is too high
this breaks the circuit for safety

38
Q

what are two advantages of a circuit breaker over a fuse?

A

can be rest

and are quicker to break the circuit

39
Q

how do the fuse and earth wire prevent a fire?

A

a large current goes from the live wire to the earth wire which cause the fuse to melt

40
Q

what is the purpose of two core cable?

A

to double insulate the appliance

41
Q

how and why does a fuse break a circuit

A

when the current is too large then the wire inside the fuse melts breaking the circuit

42
Q

how is energy wasted when there is a large current?

A

it is lost as heat to the surroundings

43
Q

what is energy in terms of pd and charge?

A

QV

physics (8 decks)

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