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Harris Academy N4 Physics > Electricity > Flashcards

Flashcards in Electricity Deck (116)
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1

What is current?

The charge transferred per second

2

What is meant by the potential difference (voltage) of a supply?

It is the number of Joules of energy given to each coulomb of charge passing through the cell

3

Which device measures current?

Ammeter

4

Which device measures voltage?

Voltmeter

5

Which device measures resistance?

Ohmmeter

6

What is the symbol for an ammeter?

Circle with an A in it.

7

What is the symbol for a voltmeter?

Circle with a V in it

8

What is the symbol for an Ohmmeter?

Circle with an Omega in it

9

How should an ammeter be connected to measure the current in a component?

It should be connected in series with the component

10

How should a voltmeter be connected to measure the voltage across a component?

It should be connected across the component

11

How can you identify a series circuit?

It is a circuit with only one path round it.

12

What is the rule for current in a series circuit?

The current is the same everywhere

I1=I2=I3

13

What is the rule for voltages in a series circuit?

The voltage across each component added together is equal to the supply voltage.

Vs=V1+V2+ ...

14

What happens if you unscrew one of the lamps in the circuit below? Why?

The other lamps go out. There is a break in the circuit and the current does not have a complete route to the battery.

15

If you heat a conductor, what happens to it's resistance?

It increases

16

How can a parallel circuit be identified?

It is a circuit with more than one path round it.

17

What is the rule for current in a parallel circuit?

The supply current is equal to the current in each branch added together.

 

IS = I1+I2+...

18

What is the rule for voltages in a parallel circuit?

The voltage across each branch is equal to the supply voltage.

VS=V1=V2= ....

19

Which circuit component is represented by the following diagram?

Cell

20

Which circuit component is represented by the following diagram?

Battery

21

Which circuit component is represented by the following diagram?

Switch

22

Which circuit component is represented by the following diagram?

Lamp

23

Which circuit component is represented by the following diagram?

Motor

24

Which circuit component is represented by the following diagram?

Loudspeaker

25

Which circuit component is represented by the following diagram?

Resistor

26

Which circuit component is represented by the following diagram?

Variable Resistor

27

Which circuit component is represented by the following diagram?

Thermistor

28

Which circuit component is represented by the following diagram?

Light Dependent Resistor

29

Which circuit component is represented by the following diagram?

Fuse

30

Which circuit component is represented by the following diagram?

Diode

31

Which circuit component is represented by the following diagram?

Light Emitting Diode

32

Which circuit component is represented by the following diagram?

Photovoltaic cell / solar cell

33

Which circuit component is represented by the following diagram?

Microphone

34

What is the energy chage in a battery?

Chemical to electrical

35

What is the energy change in a lamp?

Electrical to light (+ heat)

36

What is the energy change in a motor?

Electrical to kinetic

37

What is the energy change in a loudspeaker?

Electrical to sound

38

What is the energy change in a buzzer?

Electrical to sound

39

What is the energy change in an LED?

Electrical to light

40

What is the energy change in a photovoltaic cell?

Light to electrical

41

What is the energy change in a microphone?

Sound to electrical

42

What happens if you increase the resistance in a circuit?

The current will decrease

43

State two place a variable resistor can be used.

Light dimmer switch sped control on Scalextric cars volume control on a radio

44

State a device that can be used in a temperature sensor

Thermistor

45

State a device that can be used in a light sensor

LDR

46

What is a thermistor?

A resistor whose resistance changes with changes in temperature

47

What is a Light Dependent Resistor?

A resistor whose resistance changes with changes in light level

48

What is a fuse?

Safety device that protects the flex

49

Explain how a fuse works.

A fuse is a thin wire. If too much current passes through it, it will get hot and melt. This breaks the circuit.

50

How should a diode or LED be connected with a battery to light correctly?

Small line on battery points to small line on LED or diode.

51

Why is an LED normally connected in series with a resistor?

Resistor is to protect the LED by limiting the current in the LED.

52

What is the rule for selecting a fuse from a power rating?

Appliances less than 720W use a 3A fuse Appliances more than 720W use a 13A fuse

53

What is power?

The energy transferred  per second

54

What two factors effect the running cost of an appliance?

The time it is used for The power rating of the appliance

55

How can power losses be reduced in transmission lines?

By increasing the transmission voltage and so decreasing teh transmission current. Power loss P = I2R, so if the current is reduced the power lost is reduced.

56

Suggest a way that we say 'energy is lost' (not converted to the type of energy we want)?

  • Heat lost to the surroundings due to friction
  • Sound energy lost to air because of vibrations
  • Energy lost as heat to the surroundings
  • Heat lost in heating up a container instead of the substance in it

57

What happens if you unscrew one of the lamps in a parallel circuit?

Other lamps stay on as they still have a complete route to the battery.

58

What is the stated value of the mains?

230V, 50Hz

59

When would you use a relay?

To switch on a high current ciruit using a low current circuit for safety.

60

How does a relay work?

  • Close a switch to make a current flow in a wire.
  • This creates an electromagnet.
  • Electromagnet attracts metal switch.
  • This completes the second circuit and the lamp switches on.

61

Which component does the symbol represent?

Buzzer

62

What is the energy change in a buzzer?

Electrical to sound

63

What is meant by an analogue device?

A device that can take any value over a range

64

What is meant by a digital device?

A device that is either ON or OFF or can only take set values.

65

Name a digital input device.

Switch

66

Name an analogue input device.

LDR, Thermistor, microphone, solar cell

67

Name a digital output device

LED

68

Name an analogue output device

Loudspeaker, motor, lamp

69

Name an everyday device that gives an analogue reading.

A clock with hands, speedometer in car, analogue meter (has an arm that moves to give the reading)

70

Name an everyday device that gives a digital reading.

Digital clocks, digital stopwatch, multimeter readings

71

Suggest an output device that could give light out as a warning.

Lamp or LED

72

Suggest an output device that could make a sound as a warning.

Buzzer or Loudspeaker

73

Suggest an output device that could cause a fan to operate or to generate movement.

Motor

74

Suggest an imput device that could detect changes in temperature

Thermistor

75

Suggest an input device that could detect changes in light level

LDR (Light Dependent Resistor)

76

How would you work out total resistance in a series circuit?

Add the resistances together

RT=R1+R2+R3

77

Which logic gate is this?

AND

78

Which logic gate is this?

OR

79

Which logic gate is this?

NOT

80

When will an AND gate give a '1' or ON out?

When Input 1 AND Input 2 are ON or at '1'

81

When will an OR gate give a '1' or ON out?

When Input 1 is ON '1' OR Input 2 is ON '1' OR when Input 1 and Input 2 are ON '1'

82

How does a NOT gate work?

Put in an ON '1', get out an OFF '0'

Put in an OFF '0', get out an ON '1'

83

State Ohm's Law

V = IR

Voltage = Current x Resistance

84

State two methods of generating electrical energy

  • Solar cells
  • Wind turbines
  • Nuclear power station
  • Hydro electric

85

State an advantage of generating electrical energy by using wind turbines.

  • Does not produce greenhouse gases
  • Renewable so it will not run out

86

State a disadvantage of generating electrical energy by using wind turbines.

  • It may not always be windy enough to generate enough electrical energy
  • People object to them as they spoil the landscape

87

State an advantage of generating electrical energy by using solar cells.

  • Does not produce greenhouse gases
  • Renewable so it will not run out

88

State a disadvantage of generating electrical energy by using solar cells.

  • Many not have enough daylight to generate enough electrical energy
  • Can be expensive to install 

89

State an advantage of generating electrical energy by using nuclear power.

  • Does not produce any greenhouse gases
  • Produces a large amount of energy per kg of fuel
  • Fuel cells can be reprocessed an used again

90

State a disdvantage of generating electrical energy by using nuclear power.

  • Produces radioactive waste
  • The waste must be stored for hundreds of years
  • Expensive to build and decomission
  • If there is an accident radioactive material can be released into the environment

91

State an advantage of generating electrical energy by using hydro-electric.

  • Does not produce any greenhouse gases
  • The water is not used up in the process

92

State a disadvantage of generating electrical energy by using hydro-electric.

  • A dam must be built and land is flooded to create the water storage, this can damage the environment
  • Loss of control of water flow down stream

93

Which type of appliances consume the most energy?

Ones that are used for heating - kettle, electric shower etc.

94

What is the efiiciency of a device a measure of?

How good an appliance is at converting the input energy to the wanted output energy.

 A lamp converts electrical energy to light and heat, it would be more efficient if it did not produce heat.

95

How do you calculate efficiency?

Efficiency = (Useful energy out / Energy In ) x 100

OR

Efficiency = (Useful Power Out / Power In) x 100

96

If a power station is efficient, what is this on the environment?

  • Conserves resources (less input energy required to give the same output)
  • This can also reduce the impact on the environment

97

What do the magetic field lines round a bar magnet look like?

98

What do the field lines look like round two bar magnets?

99

What do the field lines look like round two bar magnets?

100

State two practical users of electromagnets.

  • Relays
  • Electric Bells
  • Loudspeakers
  • Fire door retainers
  • Maglev Trains

101

Why do we sometimes use an electromagnet instead of a permanent magnet?

An electromagnet can be switched on and off.

102

How can an electromagnet be constructed?

Wire wrapped wrapped round an iron nail. The ends of the wire connected to a battery.

103

How can the strength of an electromagnet be varied?

  • More turns of wire = stronger electromagnet
  • Less turns of wire = weaker electromagnet
  • Increase the current through the wire / voltage across the wire = stronger magnet
  • Decrease the current through the wire / voltage acrossthe wire = weaker magnet

104

What is the purpose of a transformer?

To increase or decrease a voltage

105

What does a step up transformer do?

Increases the voltage

106

What does a step down transormer do?

Decreases the voltage

107

Why are transformers used in electrical transmission lines?

To step up the voltage. This decreases the current and reduces the power lost in the transmission lines. At the other end a step down transformer reduces the voltage ready for use in the home.

108

What are the main parts of a transformer?

Primary Coli, Secondary Coil, Iron core

109

Give one advantage of using overhead cables.

  • Easy to access for repairs.
  • Easy to spot where a repair is required

110

Give a disadvantage of overhead cables.

  • They can look ugly in the countryside
  • High winds, heavy snow can bring them down

111

Give an advantage of underground cables.

  • They cannot be seen so do not effect the landscape
  • Will not be effected by snow or heavy winds

112

Give a disadvantage of underground cables

  • Have to dig them up for a repair
  • More difficult to find breaks

113

In a traditional power station (coal, gas or oil fired)  what are the main parts that help produce electrical energy?

  • Boiler
  • Turbine
  • Generator

114

What is the energy change in a boiler?

Chemical to heat

115

What is the energy change in a turbine? (Traditional power station)

Heat to Kinetic

116

What is the energy change in a generator?

Kinetic to electrical