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new physics year 10 > topic 2 > Flashcards

topic 2 Flashcards

1
Q

what is the national grid

A

a giant system of cables and transformers that covers the UK and connects power stations to consumers

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2
Q

what does the national grid transfer

A

electrical power from power stations anywhere on the grid (the supply)to anywhere else on the grid where it’s needed (the demand)

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3
Q

to transmit the huge amount of power all over the uk what needs to be done

A

you need either a high potential difference or a high current

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4
Q

what is the problem with high current

A

is that you lose loads of energy as the wires heat up and energy is transferred to the thermal energy store of the surroundings

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5
Q

what is done in the N.G to keep costs low

A

boosting up the p.d up really high (40,000v) and keeping the current as low as possible

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6
Q

for a given power, what happens when you increase the p.d

A

you decrease the current, which decreases the energy lost by heating the wires and the surroundings

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7
Q

why is energy always lost in the power cables

A

because of the resistance of the wires

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8
Q

the bigger the difference between the power stations and the homes…

A

the greater energy loss

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9
Q

what can be used to reduce the energy loss

A

use transformers

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10
Q

what happens first, what transformer does the electricity pass through

A

the step-up transformer which increase the p.d to several hundred thousand volts

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11
Q

after passing through the step-up transformer, where does the electricity pass through

A

the high voltage cables

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12
Q

why does electricity pass through the step-up transformer

A

because less energy is lost in the power cables when the p.d is very high

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13
Q

from the step-up transformer to the high voltage cables, where does electricity pass through next

A

step-down transformer

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14
Q

why does electricity pass through step-down transformers

A

because the potential difference is too high and too dangerous to pass through to homes

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15
Q

what does the step-down transformer do

A

the electricity passes through here which reduce the potential difference to about 230 V

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16
Q

how is energy transferred between stores

A

electrically by electrical appliances

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17
Q

what are the 2 types of electricity supply

A

alternating and direct current

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18
Q

what happens to the current in alternating supplies

A

it is constantly changing direction

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19
Q

how are alternating currents produced

A

by alternating voltages in which the positive and negative ends keep keep alternating

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20
Q

what type of electricity supply is the uk mains supply

A

an alternating current at around 230 V

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21
Q

what is the frequency of the ac mains supply

A

50 Hz

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22
Q

what type of electricity do batteries and cells supply

A

direct current

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23
Q

what is direct current

A

s current that is always flowing in the same direction, it’s created by a direct voltage

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24
Q

most cables have how many wires

A

3

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25
Q

give the names of the 3 types of wires

A

1) live wire
2) neutral wire
3) earth wire

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26
Q

how are most electrical appliances connected to the mains supply and what does it mean

A

by 3 core cables, it means that they have 3 wires inside them, each with a core of copper and a coloured plastic coating

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27
Q

the 3 core cables have a core of what

A

copper

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28
Q

what colour is the live wire

A

brown

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29
Q

what current does the live wire provide

A

an alternating current at about 230 V from the mains supply

30
Q

what colour is the neutral wire

A

blue

31
Q

what does the neutral wire do

A

completes the circuit and carries away current

32
Q

what voltage is the neutral wire at

A

0V

33
Q

what colour is the earth wire

A

yellow and green

34
Q

what does the earth wire do

A

it protects the wiring for safety- it stops the appliance casing from becoming live

35
Q

what voltage is the earth wire at

A

0V

36
Q

what happens when a human touches a live wire

A

our bodies are at 0V and if we touch the live wire a large P.D is produced across your body and a current flows through you

37
Q

why is the live wire dangerous for humans

A

it can give you an electrical shock, injure or even kill you

38
Q

why is any connection between the earth and live wire dangerous

A

if the link creates a low resistance path to earth, a huge current will flow, which could result in a fire

39
Q

what is an electrical current

A

a flow of electrical charge around a circuit

40
Q

if we close a switch in a series circuit what happens to the electrons

A

electrons flow out of the cell and move around the circuit

41
Q

what are the flow of electrons that move out of the cell called

A

an electric current

42
Q

in a series circuit how does the electric current flow

A

from the negative end of the cell to the positive end

43
Q

in a series current what happens to the potential difference

A

it is shared between the various components, so the potential difference round a series circuit always adds up to equal the source p.d

44
Q

in a series circuit what happens to the current

A

the same current flows through all the components

45
Q

how is the size of the current determined by in a series circuit

A

by the total p.d of the cells and the total resistance of the circuit i.e. I + V/R

46
Q

how do you work out the total resistance in a series circuit

A

it is the sum of the resistances in the series circuit

47
Q

the bigger a component’s resistance in a series circuit …

A

the bigger its share of the total p.d

48
Q

what happens to the p.d in PARALLEL circuits

A

all of the circuits get the full source p.d so the p.d is the same across all components

49
Q

so if you connect a bulb in a parallel circuit what happens to the light of the bulbs

A

they will both be the same

50
Q

what is the total current in parallel circuits

A

the total current flowing around the circuit is equal to the total of all the currents through the separate components

51
Q

what happens to the current in parallel circuits when at a junction

A

it splits or rejoins

52
Q

what happens if you have 2 resistors in parallel

A

their total resistance is less than the resistance of the smallest of the 2 resistors

53
Q

how will electrical charge flow round a complete circuit

A

if there is a p.d

54
Q

what is the unit of current

A

ampere, A

55
Q

describe the current in a single, closed loop

A

the current has the same value everywhere in the circuit

56
Q

what is potential difference

A

(voltage) the driving force that pushes the charge around

57
Q

what is the unit for p.d

A

V

58
Q

what is resistance

A

anything that slow the flow of p.d down

59
Q

the greater the resistance across a component, ….

A

the smaller the current that flows

60
Q

what is size of current

A

the rate of flow of charge

61
Q

what happens when a current flows through an ohmic conductor at a CONSTANT TEMP

A

it is directly proportional to the p.d across it

62
Q

what happens when an electrical charge flows through a filament lamp

A

it transfers some energy to the thermal energy store of the filament, which is designed to heat up

63
Q

what happens to the resistance in a filament lamp

A

resistance increases with temperature, so as the current increases, the filament lamp heats up more and the resistance increases

64
Q

what does resistance in a diode depend on

A

the direction of the current

65
Q

what is an LDR

A

a resistor that is dependant on the intensity of light

66
Q

in a bright light, what happens to the resistance

A

it falls

67
Q

in darkness, what happens to the resistance

A

it is at it’s highest

68
Q

what is a thermistor

A

a temp dependant resistor

69
Q

what happens to the resistance in hot conditions

A

it drops

70
Q

what happens to the resistance in cool conditions

A

it goes up

71
Q

what do thermistors make that are useful

A

temp detectors

new physics year 10 (4 decks)

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