Electricity Flashcards
(115 cards)
1
Q
What are conductors?
A
Materials that allow flow of electrical charge.
2
Q
What is an example of a good conductor?
A
Metals.
3
Q
What are insulators?
A
Materials that do not allow flow of electrical change.
4
Q
What is an example of a good insulator?
A
Plastic.
5
Q
How are metals able to conduct electricity?
A
Have free electrons which can move and carry a charge, allowing current to flow.
6
Q
Why do cables have plastic coatings?
A
To prevent electric shocks as wires can be very dangerous.
7
Q
What is conventional current?
A
Current moving from positive terminal of cell/battery around circuit to negative terminal.
8
Q
What is electron flow?
A
Current moving from negative terminal of cell/battery around circuit to positive terminal.
9
Q
What does the long part of a cell showcase?
A
Positive terminal.
10
Q
What does the short part of a cell showcase?
A
Negative terminal.
11
Q
What is an electric circuit?
A
Path for electric charge to flow along.
12
Q
What is needed for an electric circuit to work?
A
Source of energy
A complete loop
A component
No short circuits.
13
Q
What happens if the circuit is broken in a series circuit?
A
Current will not flow.
14
Q
What is a short circuit?
A
Current that can flow along a path without passing through components in a circuit.
15
Q
What does the cell in a circuit provide?
A
Push necessary to make electrons flow.
16
Q
What is the equation for current?
A
I = Q / t
17
Q
What is the equation for Ohms law?
A
V = R x I
18
Q
What does the gradient of a V-I graph tell us?
A
The restistance of the wire.
19
Q
What does a small gradient on a V-I graph tell us?
A
Low resistance.
20
Q
What does a large gradient on a V-I graph tell us?
A
High resistance.
21
Q
What does the gradient of a I-V graph tell us?
A
1 / resistance.
22
Q
What does a small gradient on a I-V graph tell us?
A
High resistance.
23
Q
What does a large gradient on a I-V graph tell us?
A
Low resistance.
24
Q
How are ammeters connected in a circuit?
A
In series.
25
How are voltmeters connected in a circuit?
In parallel.
26
What is special about the gradient on a V-I graph for an ohmic conductor?
Constant
27
If the gradient on and V-I graph for an ohmic conductor is constant, what can be said about the resistance?
Constant
28
What does the gradient of an I-V graph being constant show?
Resistance of metallic conductor at constant temperature is constant.
29
What is an ohmic conductor?
One in which potential difference (p.d.) is directly proportional to current passing through it provided material is maintained at constant temperature.
30
What should an ohmic conductor graph contain?
Straight line passing through origin.
31
What is an example of an ohmic conductor?
Metal at constant temperature.
32
How can current be described in a circuit?
Current flowing through series circuit is same everywhere.
33
How can voltage be described in a circuit?
E in = E out
Supply voltage = V1 + V2 + V3
34
What is current split?
Current going into a junction is equal to current out of the junction.
35
What is voltage split?
Each branch of parallel circuit has same voltage applied to it.
36
How can current and voltage be described in a series circuit?
Current stays same but voltage splits up.
37
What is the equation for total resistance in a series circuit?
RT = R1 + R2
38
How can current and voltage be described in a parallel circuit?
Voltage stays same but current splits up.
39
What is the equation for total resistance in a parallel circuit?
1/RT = 1/R1 + 1/R2
40
What is special about the total resistance in a parallel branch?
Total resistance is always smaller than smallest resistor in branch.
41
What happens when a length of wire is maintained at constant temperature?
Resistance and length directly proportional to each other.
42
What 2 key requirements would a graph need to show for the resistance and length of a metal wire being directly proportional to each other?
Straight line
Passing through the origin
43
In a metal wire at constant temperature, what is the relationship between the cross sectional area and the resistance?
Resistance is inversely proportional to cross sectional area.
44
What is the difference in resistance between a conductor and an insulator?
Conductor - low resistance
Insulator - high resistance
45
What does a conductor have a low resistance?
It has free electrons.
46
What is an electrical current?
Electrons flowing through metal wire.
47
What is the main type of energy produced when electrical current travels through a wire?
Thermal energy
48
How is thermal energy produced when electrical current travels through a wire?
Free electrons flowing through collide with atoms of wire causing them to lose their kinetic energy and making atoms vibrate more and heat wire up.
49
What is the equation for energy in Electricity?
E = P x t
50
What are the quantities involved in E = P x t?
E = energy in joules / J
P = power in watts / W
t = time in seconds / s
51
What is the equation for power in electricity?
P = I x V
52
What are the quantities involved in P = I x V?
P = power in watts / W
I = current in amperes / A
V = voltage in volts / V
53
What is a fuse?
Electrical appliance used to prevent user from an electrical shock.
54
How does a fuse prevent the user from getting an electrical shock?
When larger current than rating of fuse passes through it, wire of fuse melts.
Breaks the circuit so stops user from getting electrical shock.
55
What are the 2 types of electrical current?
Direct current (D.C.)
Alternating current (A.C.)
56
What is direct current?
One-way flow of electrons from negative to positive terminals of power supply.
57
What is alternating current?
Oscillation of electrons or ‘back and forward’ movement.
58
What equation tin is used to display A.C. Waveforms?
Oscilloscope
59
How often does an alternating current change direction?
50 times every second.
60
What is the frequency for alternating current?
50Hz
61
What is the unit used for the amount of energy used in our homes?
Kilowatt-hour
62
What are the quantities involved in the E = P X T for kilowatt-hour?
E = energy in kilowatt-hours / kWh
P = power in kilowatts / kW
t = time in hours / h
63
What does 1 kilowatt-hour mean?
Energy transferred by 1kWh appliance operating for 1 hour.
64
What does 1 kilowatt-hour represent?
1 unit of electricity.
65
What is the equation for determining the number of units of electricity used in your home?
Number of units = Current meter reading - Previous meter reading
66
What is the equation for the cost of electricity?
Cost = Number of units x Unit price
67
What happens when a switch is turned on in a circuit?
Two terminals are connected so current will flow through circuit.
68
What happens when a switch is turned off in a circuit?
Circuit is broken so there is no contact between terminals so no current will flow.
69
Where is a switch placed in a circuit?
On positive or live side of circuit.
70
What are the 2 types of switch?
One-way switch
Two-way switch
71
When is a one-way switch used?
To switch light from just one place.
72
Where is a one-way switch usually used?
Beside a door.
73
When is a two-way switch used?
To control light from two locations inside a building.
74
Where is a two-way switch usually used?
On staircase
In long hallway
75
What happens when both switches are up in a circuit?
Circuit is complete, current flows and lamp lights.
76
What happens when only one of the switches are up in a circuit?
Circuit is broken, current stops flowing and lamp is off.
77
What is a 3-pin plug?
Plug consisting of three pins, live, neutral and earth.
78
What colour is the live wire in a 3-pin plug?
Brown
79
What is the purpose of the live wire in a 3-pin plug?
Connected to fuse on live pin.
Electrical current uses live wire at its route in.
80
What colour is the neutral wire in a 3-pin plug?
Blue
81
What is the purpose of the neutral wire in a 3-pin plug?
Route electric current takes when it exits appliance so has voltage close to 0.
82
What colour is the earth wire in a 3-pin plug?
Green and yellow
83
What is the purpose of the earth wire in a 3-pin plug?
Connected to earth pin.
Used when appliance has metal casing to take any current away if live wire comes in contact with casing.
84
Is double circulation?
Appliances having no earth wire so have plastics casings to prevent an electric shock.
85
What do the arrows on magnetic field lines indicate?
Direction North Pole would take at that point.
86
What does the distance between the magnetic field lines tell us?
How strong field is.
87
What is the magnetic field verbs strong on a magnet?
At both poles.
88
How is a magnetic field produced?
Electrons spinning and orbiting in a wire.
89
What is the right hand grip rule used for?
Determine poles in current carrying wire in solenoid form.
90
What does the thumb indicate in the right hand grip rule?
Conventional current flow.
91
What does the direction of the fingers incite in the right hand grip rule?
Direction of flow.
92
What if Fleming’s left-hand rule used for?
Predict direction of force acting on wire (its motion) if direction of current and magnetic field are known.
93
What does the thumb represent in Fleming’s left-hand rule?
Direction of force (motion).
94
What does the index finger represent in Fleming’s left-hand rule?
Direction of magnetic field lines (north to south).
95
What does the middle finger represent in Fleming’s left-hand rule?
Direction of conventional current.
96
What electrical device is based on the arrangement of a coil and a magnet in an electromagnet?
Electrical generator.
97
Who and when independently discovered the reverse process of creating an electric current via a magnetic field?
Faraday (England) and Henry (USA) in 1831.
98
What electromagnetic induction?
When wire cuts lines of mag tied field and electromotive force (EMF) is included.
99
How is the EMF increased when generating electricity?
Move wire faster.
Use stronger magnet.
Use coil of wire and increase number of turns.
100
What happens when the wire slowly cuts the lines of a magnetic field to produce EMF?
Small deflection on ammeter.
101
Why is a small deflection produced on the ammeter when the wire cuts the lines of a magnetic field to produce an EMF?
Small number of flier lines cut per second.
102
What happens when the wire quickly cuts the lines of a magnetic field to produce EMF?
Large deflection.
103
Why is a large deflection produced on the ammeter when the wire cuts the lines of a magnetic field to produce an EMF?
Cutting more fluid lines per second.
104
How would you use a bar magnet and a coil to produce an a.c. current?
Move bar magnet in and out of coil, cutting magnetic field lines.
As magnet is being moved back and forth, changes direction of current, creating a.c. current.
105
What is the summary for using d.c. for a transformer?
1. Push switch down so field lines cut.
2. Hold switch down until no more field lines cut.
3. Release switch so field lines cut again for split second.
106
What is a transformer?
Device sued to transfer energy across grid in most efficient manner possible.
107
What does an a.c. generator of electricity consist of in its simplest form?
Coil of wire rotated better poles of magnet.
108
What are the steps involved of transferimg electricity across a grid?
1. Power station
2. Step-up transformers
3. High voltage transmission lines
4. Step-down transformers
5. Consumers, e.g. homes, factories, shops
109
How does a step-up transformer work?
Primary voltage stepped up in secondary coil which has greater number of turns N.
By stepping up voltage, current is reduced.
Reduces power losses in cables, as P = I2^ x R.
110
How does a step-down transformer work?
Primary voltage stepped down in secondary coil which has less number of turns N.
By stepping down voltage, current is increased.
Voltage now suitable for use, such as 240V in homes.
111
What is the equation for a transformer?
Ns / Np = Vs / Vp
112
What are the quantities involved in the equation Ns / Np = Vs / Vp?
Ns = number of turns on secondary
Np = number of turns on primary
Vs = voltage across secondary
Vs = voltage across primary
113
What is the equation Ns / Np = Vs / Vp equivalent to?
Power into primary = power out of secondary
114
What is the equation for power into primary = power out of secondary in a transformer?
Ip x Vp = Is x Vs
115
What are the quantities invoked in the equation Ip x Vp = Is x Vs?
Ip = current in primary
Vp = voltage of primary
Is = current in secondary
Vs = voltage of secondary
