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science > year 2 chap 13 > Flashcards

year 2 chap 13 Flashcards

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1
Q

what are electrical systems?

A

an object made up of various electrical components that allow for transporting electrical energy

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2
Q

when people invent or construct electrical appliances, what do they use to represent their designs?

A

diagrams

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3
Q

what do the diagrams include?

A

the symbols that represent different components of an electrical system

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4
Q

what is a cell in an electrical system?

A

an energy source

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5
Q

shorter line in the circuit symbol for the cell is the ___ of the cell and the longer line is the ___ of the cell

A

negative side ; positive side

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6
Q

what type of circuit is it if the switch is open and the bulb does not light up?

A

an open circuit

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7
Q

what type of circuit is if the switch is closed the bulb lights up?

A

a closed circuit

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8
Q

current can only flow in ___ direction

A

one

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9
Q

current flows from ‘positive to negative’ or ‘negative to positive’

A

positive to negative

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10
Q

what are the main components of an electrical system?

A
  • cell
  • electric charge
  • wires
  • electrical device (e.g bulb)
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11
Q

how many paths for electrical current are there in a series circuit?

A

1

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12
Q

how many paths for electrical current are there in a parallel circuit?

A

more than 1

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13
Q

are the brightness of the bulbs in a series circuit brighter or dimmer when there is only one battery for two bulbs to share?

A

dimmer

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14
Q

are the brightness of the bulbs in a parallel circuit brighter or dimmer when there is only one battery for two bulbs to share?

A

brighter

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15
Q

is the brightness of a bulb connected in series in a parallel circuit brighter or dimmer than the other bulbs connected in parallel?

A

brighter

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16
Q

the rate at which electric charge flows is known as the __

A

electric current, I

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17
Q

what is the SI unit for electric charge?

A

ampere (A)

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18
Q

how can we measure the current flowing in an electric circuit?

A

using an ammeter

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19
Q

measurement of an electric current indicates ___

A

how much electric charge is flowing past a particular point in an electric circuit per unit time

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20
Q

in an electric circuit, why is there the flow of electric charge?

A

because of the movement of electrons in the electrical conductors

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21
Q

the greater the flow of electric charge per unit time, ‘the larger the current’ or ‘the smaller the current’

A

the larger the current

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22
Q

to measure the current flowing through a circuit, an ammeter is connected in ‘series’ or ‘parallel’ within a circuit

A

series

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23
Q

what is potential difference?

A

the amount of energy needed to move a unit charge from one point in an electric circuit to another point

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24
Q

what can the amount of energy needed to move a unit charge from one point in an electric circuit to another point also be referred to as?

A

voltage

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25
Q

what does a voltmeter do?

A

it measures the potential difference between two points in an electric circuit

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26
Q

what is the SI unit of potential difference?

A

volt (V)

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27
Q

to measure the potential difference across an electrical component such as a bulb, a voltmeter is connected ‘in series’ or ‘in parallel’ to the electrical component?

A

in parallel

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28
Q

what is electrical resistance?

A

a measure of how much the component opposes the flow of electric current

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29
Q

conductors of electricity have __ resistance to current

A

low

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30
Q

insulators of electricity have __ resistance to current

A

high

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31
Q

what are examples of conductors of electricity?

A

copper and silver

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32
Q

what are examples of insulators of electricity?

A

plastic and glass

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33
Q

what happens when electric current flows through some conductors that have higher resistance than copper and silver?

A

much electrical energy is converted to other forms like heat and light energy, which can be used for different purposes

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34
Q

what are examples of conductors that have higher resistance than copper and silver?

A

tungsten and nichrome

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35
Q

how are these conductors that have higher resistance than copper and silver used?

A

tungsten is used to make lightbulbs

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36
Q

what is the SI unit of electrical resistance?

A

ohm (Ω)

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37
Q

what are resistors?

A

electrical components that reduce the flow of current in a circuit

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38
Q

what happens when a resistor is added to an electrical circuit?

A

it is more difficult for electric charge to flow in the circuit

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39
Q

what happens to the current and the bulb when it is more difficult for electric charge to flow in the circuit?

A

the current flowing through the bulb decreases and the bulb becomes less bright

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40
Q

what are the 2 types of resistors?

A

fixed resistor and variable resistor

41
Q

what type of resistance does a fixed resistor have?

A

fixed, non-adjustable electrical resistance

42
Q

what type of resistance does a variable resistor have?

A

a range of electrical resistance that can be adjusted

43
Q

what are fixed resistors made up of?

A

fixed resistors are made of a combination of materials

44
Q

conductors of electricity would have ‘more resistance’ or ‘less resistance’ to electric currents than insulators?

A

more resistance

45
Q

what is the resistive element made up of?

A

a mixture of fine carbon particles and a non-conductive ceramic material

46
Q

the more carbon, the ___ resistance

A

less

47
Q

why are resistors used in circuits?

A

resistors are used to keep the current in circuits to a safe level and prevent overheating of the circuits

48
Q

variable resistors are used in household appliances to?

A

control the current in a circuit

49
Q

what is an example of variable resistors used in household appliances?

A

variable resistors are used in dimmers that control the brightness of light in a room

50
Q

what type of resistor is a rheostat?

A

a variable resistor

51
Q

the rheostat has a ___ that can be shifted to ___ and change the amount of current in the circuit

A

slider ; adjust the resistance

52
Q

what do you call 2 cells that are placed together in an electric circuit?

A

a battery of two cells

53
Q

why are two bulbs connected in parallel usually brighter than two bulbs connected in series?

A

because in series, the voltage is shared by two bulbs but in parallel, the voltage experienced by both bulbs is the same

54
Q

what are the 3 useful effects of a current flowing in an electrical system?

A

chemical effect, heating effect and magnetic effect

55
Q

what is the chemical effect of an electric current?

A

a chemical change takes place when an electric current passes through certain chemical solutions or liquids

56
Q

how can the chemical effect of an electric current be useful?

A

this effect can be used for extracting metals or electroplating an object w. a thin layer of metal

57
Q

what is the heating effect of an electric current?

A

when an electric current is passed through a heating element, some electrical energy may be converted to heat energy

58
Q

what does a heating element consist of?

A

it consists of a wire made of a high-resistance material like nichrome

59
Q

a high-resistance material can withstand ___

A

high temperatures

60
Q

how can the heating effect of an electric current be useful?

A

some household appliances use a heating element to work, these include the hairdryer, rice cooker, toaster and kettle

61
Q

what is the magnetic effect of an electric current?

A

an electric current has an effect on magnets

62
Q

what happens when an electric current flows through a wire placed near a compass?

A

the needle in the compass is deflected

63
Q

how are electromagnets created?

A

by passing an electric current through a coil of wire, to turn it into a temporary magnet

64
Q

how are electromagnets used?

A

electromagnets can be found in robot systems assist surgeons as the force applied by a surgeon’s hand may be too great for the human body

65
Q

what causes electrical fires?

A

when an electrical circuit is damaged/overloaded, a very large amt of current may be drawn from the power supply which can result in excessive heat & cause wires to melt can even cause a fire

66
Q

what are the 2 harmful effects of electricity?

A

electrical fire and electric shock

67
Q

what is overloading?

A

when multiple plugs are inserted in the same socket

68
Q

what are wires carrying electricity to electrical appliances insulated with?

A

plastic/rubber

69
Q

why are wires carrying electricity to electrical appliances insulated with plastic/rubber?

A

to protect the user from an electric shock

70
Q

how do electric shocks happen?

A

when the insulating material is worn out, the conducting wires are exposed the user accidentally touches the exposed wires

71
Q

what are the 2 safety devices in our household electrical systems?

A

fuse and circuit breaker

72
Q

every electrical appliance has a limit to the ___ so that it can operate safely

A

max amount of current that flows through it

73
Q

what is a fuse?

A

an electrical component used to protect the electrical appliance from excess current

74
Q

what does the current rating of a fuse indicate?

A

it indicates the maximum amount of current that can flow through the fuse before the wire inside it melts

75
Q

what causes the thin wire inside the fuse to melt?

A

the current flowing through the appliance is larger than the current rating of its fuse due to an electric fault

76
Q

what happens when the thin wire inside the fuse melts?

A

the circuit becomes an open circuit & no current is able to flow through the appliance

77
Q

after the fault in the appliance is fixed, ___ before the appliance can be used again

A

the damaged fuse needs to be replaced

78
Q

what is the full name of the circuit breaker?

A

the Residual Current Circuit Breaker (RCCB)

79
Q

the circuit breaker has ___ and the switches are connected to different parts of a household

A

many individual switches

80
Q

what causes the switch linked to the appliance in the circuit breaker to trip and cut off the current?

A

when the current flow is too large due to a faulty electrical appliance

81
Q

what can the tripping of the switch in the circuit breaker prevent?

A

it can prevent electric shocks

82
Q

the RCCB can be reactivated ___ after the faulty appliance is repaired

A

manually

83
Q

how can we reduce the consumption of electrical energy in our daily lives?

A

by making choices that are energy-efficient

84
Q

what does being energy efficient mean?

A

it means to use less electrical energy to perform the same tasks

85
Q

consumption of electrical energy depends on?

A

the rate at which electrical energy is used by an electrical appliance to serve it’s function

86
Q

what is the amount of electrical energy used for conversion to other forms of energy per unit time referred to?

A

the power of an electrical appliance

87
Q

what is the SI unit of power?

A

watt (W)

88
Q

what is the monthly electrical energy consumption in our electricity bills measured in?

A

it is measured in kilowatt-hours (kWh)

89
Q

1 kW = ___ W

A

1000 W

90
Q

how to calculate kilowatt-hours?

A

electrical energy (kWh) = power (kW) x time (h)

91
Q

how much energy is needed to keep a 1000 watt (1 kW) appliance running for one hour

A

1 kWh

92
Q

1 kWh of electrical energy consumption is equal to ___ of energy

A

3 600 000 J

93
Q

how to convert watts into kilowatts?

A

the number of watts divided by a thousand

94
Q

how to calculate how much energy is being consumed in 1 kWh?

A

1 kW x 1h = 1000 W x 3600 seconds = 3 600 000 J

95
Q

how much is 80 W in kilowatts?

A

0.080 kW

96
Q

how to calculate the cost of electrical energy consumption of an electrical appliance?

A

we need to know the current electricity tariff in the location

97
Q

electricity tariff is expressed in?

A

cents per kilowatt-hour

98
Q

if an electric fan has a power rating of 60 W and the electricity tariff is 27 cents per kWh
what is the cost of electrical energy consumption of an electric fan if it is switched on for 8 hours?

A

power (kW) x time (h)
= (60 ÷ 1000) x 8h
= 0.060 kW x 8h
= 0.48 kWh
0.48 kWh x $0.27
= $0.1296

99
Q

name a way to conserve energy in households

A

buy electrical appliances that have energy labels with 3 or more ticks

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