Electricity Flashcards
To learn the content for the electricity section of the course
1
Q
What is current?
A
The charge transferred per second
2
Q
What is meant by the potential difference (voltage) of a supply?
A
It is the number of Joules of energy given to each coulomb of charge passing through the cell
3
Q
Which device measures current?
A
Ammeter
4
Q
Which device measures voltage?
A
Voltmeter
5
Q
Which device measures resistance?
A
Ohmmeter
6
Q
What is the symbol for an ammeter?
A
Circle with an A in it.
7
Q
What is the symbol for a voltmeter?
A
Circle with a V in it
8
Q
What is the symbol for an Ohmmeter?
A
Circle with an Omega in it
9
Q
How should an ammeter be connected to measure the current in a component?
A
It should be connected in series with the component
10
Q
How should a voltmeter be connected to measure the voltage across a component?
A
It should be connected across the component
11
Q
How can you identify a series circuit?
A
It is a circuit with only one path round it.
12
Q
What is the rule for current in a series circuit?
A
The current is the same everywhere
I1=I2=I3
13
Q
What is the rule for voltages in a series circuit?
A
The voltage across each component added together is equal to the supply voltage.
Vs=V1+V2+ …
14
Q
What happens if you unscrew one of the lamps in the circuit below? Why?
A
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
Q
If you heat a conductor, what happens to it’s resistance?
A
It increases
16
Q
How can a parallel circuit be identified?
A
It is a circuit with more than one path round it.
17
Q
What is the rule for current in a parallel circuit?
A
The supply current is equal to the current in each branch added together.
IS = I1+I2+…
18
Q
What is the rule for voltages in a parallel circuit?
A
The voltage across each branch is equal to the supply voltage.
VS=V1=V2= ….
19
Q
Which circuit component is represented by the following diagram?
A
Cell
20
Q
Which circuit component is represented by the following diagram?
A
Battery
21
Q
Which circuit component is represented by the following diagram?
A
Switch
22
Q
Which circuit component is represented by the following diagram?
A
Lamp
23
Q
Which circuit component is represented by the following diagram?
A
Motor
24
Q
Which circuit component is represented by the following diagram?
A
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
