Electricity Flashcards
(110 cards)
1
Q
What is electricity and what is the theory of electric charges?
A
Electricity (energy) is created when electrons flow through an object, and the theory of charges is that we can use electricity to perform many tasks
2
Q
Static Electricity
A
- A stored (not moving) charge
- Caused by friction, creates unbalanced charges by transferring electrons
- “Energy” only during discharge
3
Q
Who described charges as +/-?
A
Benjamin Franklin
4
Q
Law of Charges
A
- Like charges repel
- Opposite charges attract
- Charged objects attract neutral
5
Q
Atom
A
Nucleus (p, n) + Orbiting electrons
6
Q
Which part of atoms move freely?
A
Electrons
7
Q
Current electricity
A
Electrons moving through an object
8
Q
Insulators and Conductors
A
Objects that do not allow and allow electrons to flow freely within them respectively
9
Q
Superconductors
A
-Almost no resistance
-Usually very low temperature
-Less space, more charge, efficiency very high
10
Q
Semiconductors
A
Objects with higher conductivity than insulators but less than conductors. They usually change conductivity on a foreseeable scale due to certain factors (e.g. light, heat, pressure)
11
Q
Static discharge
A
Aka neutralizing unbalanced charges (Neutralize: To become balanced). The discharge is felt as a shock/spark. Electrons transfer to the object with more positive total charge.
The shock/spark could cause a fire, dangerous if high current
12
Q
Physically prevent static electricity?
A
Antistatic sprays
13
Q
Charge separation
A
-Friction causes electrons based on their triboelectric series (easily lost –> lose, not easily lost –> gain)
14
Q
1.2 Circuits and composing parts
A
- 4 Parts: Control (switch), load (bulb/motor), conductor (wires), source (cell/battery)
- Closed flow
(Cells in battery must be in correct order or circuit source does not function)
15
Q
What is a circuit?
A
Closed pathway where electrons can flow freely (also flow movement caused by voltage)
16
Q
Cell vs Battery
A
One vs series of multiple cells together
17
Q
Types of switches
A
Transistors (Rheostats), normal switch, multi-way
18
Q
Units
A
- Current: Ampere A (André-Marie Ampère
- Charge: Coulomb C (Charles Augustin de Coulomb)
or Elementary charge e - Voltage: Volt V (Alessandro Volta)
- Resistance: Ohm Ω (Georg Ohm)
- Induction: Henry H (Henry Lenz)
- Resistivity: Ohm-meters (Ωm)(distance*Resistance)
- Conductivity: Siemens/meter (Werner von Siemens) S/m (aka mho/m or ℧/m, same thing)
- Conductance: ℧ mhos or S Siemens
- Capacitance: Farads, F (Michael Faraday)
- Work: Joules J or kilowatt hours kWH (James Prescott Joule)
- Power: Watts W or kilowatt kW (James Watt)
19
Q
What is electric current?
A
- “Intensity” of the flow of electrons
- Similar logic to flow rate (NOT SPEED)
- Flow rate: m^3/s or m^2*(m/s)
- m^3: “Volume” of charge passing through (Coulombs)
- s: How much time it takes
- m^2: Area of uniform surface
- m/s: Drift velocity of electrons
- Not mass (just how much “charge” they fill up)
- REAL FORMULA:
I = A_s × v_drift × n × e
Let number value of area = a
Let drift velocity = b
Let #electrons = c
I = (a)m^2 × (b)m/s × (c)/m^3 × 1.602176634 ×10^-19C
I ≈ abc × 1.6 × 10^-19 (C/s) (Where abc1.610^-19 is the value of the electric current)
THERMAL VELOCITY OF ELECTRONS IS ALMOST LIGHT SPEED WHILE DRIFT VELOCITY IS THE EFFECT OF THE ELECTRIC FIELD, WHICH IS ONLY LIKE A MILLIMETRE PER SECOND
20
Q
What is voltage?
A
Difference in “potential” between two points in a circuit (VOLTAGE IS NOT ENERGY), amount of work per unit charge
21
Q
Symbols
A
Current: I
Voltage: V
Resistance: R
Resistivity: ρ
Conductance: G
Conductivity: σ
Inductance: L (Henry Lenz)
Capacitance: C
22
Q
What are the tools we use in this unit and their purposes?
A
R: Ohmmeter
I: Ammeter/Galvanometer
V: Voltmeter
All: Multimeter
23
Q
Formulas:
A
P=IV
V=IR
C=Q/V
GR=1
σρ=1
I=Q/t
V=W/Q
Pt=W (E for energy or W for work same thing)
(OR P=E/t or P=W/t)
e=1.602176634*10^-19C
24
Q
Water Wheel analogy
A
Pipes = Conductor
Water = Electric current
Water wheel = Load
Pump/Reservoir = Source
Difference in height = Voltage
Valves = Switches
Anything that affects how bad/slowly the water flows = Resistance
25
Series circuit
Circuit with one route
26
Parallel circuit
Circuit with multiple routes, each route is a single series circuit
27
How is household electricity wired?
Parallel
28
Using a multimeter
Red = Positive, Black = Negative, 10 second rule: do not hold in current for more than 10 seconds
29
Factors and formula for resistance
R=ρ(T)*(L/A)
(Length * Area * Function of resistivity at certain temperature)
ρ(T) = ρ_0[1+α(T-T_0)]
- ρ_0: Function is resistivity at 0°C
- α: Temperature coefficient/constant of resistivity, 1/°C, RATE of how resistivity increases with temperature
- T: Object current temperature
- T_0: Reference temperature where ρ_0 is known (Usually 20°C or 0°C)
Factors: Temperature, length, gauge, material (all increase with resistance except for gauge)
30
How do we connect our tools in a circuit?
Ammeter: Series
Voltmeter: Parallel
Ohmmeter: Depends on what type
31
What does a fuse do?
Melts if circuit current too high, breaks current to prevent damage
32
How should a circuit be drawn?
Rectangle(s)
33
What are thermocouples and how do they work?
- Conversion: Heat to electricity
- Uses difference in temperature in metals to create current (1 hot 1 cold)
- Loop of two metal wires connected together
- Can be used as a temperature sensor
34
What are thermopiles and how do they work?
- Conversion: Heat to electricity
- Multiple thermocouples stacked together
- Seebeck effect
35
Thermo-electric generator
- Conversion: Heat to electricity
- Generator uses cooling fan and other tech while transferring and outputting the thermopile current for use in a circuit with the load
36
How do household appliances (e.g. toaster, stove, non-LED lightbulb) work?
- Conversion: Electricity to heat
- By resisting the current, the appliance produces heat
37
Piezoelectric effect description?
- Conversion: Electricity to Mechanical
- When a solid like quartz forms a potential difference, it starts vibrating
- Phone alarms
- Watches
38
Who discovered the piezoelectric effect?
Pierre and Jacques Curie
39
How does a BBQ lighter work?
- Conversion: Mechanical to Electrical to Thermal to Thermal and Light (chemical reaction converts chemical to thermal, the two routes meet at thermal)
- Pushing the lighter pushes the piezoelectric crystal which causes a spark in the circuit, and the spark ignites the butane
- Reverse piezoelectric effect
40
How do LEDs work?
- Conversion: Electricity to Light
- Light emitting diodes have semiconductor components that only allow current to come in one way to light the diode; they glow when electricity runs through
41
How do photovoltaic cells work and how are they drawn?
- Circle with two vertical lines and horizontal rectangles
- Device that produces electricity when light hits it (by empowering electron flow)
- Light to electricity
42
How was the first electrochemical cell invented?
Alessandro Volta wanted to reprimand the unlikely theory of "animal electricity" by Luigi Galvani, so he used a wet cell to generate voltage (metals + acid/salt solution), if you put many discs it would form a battery
43
Parts of an electrochemical cell and its conversion description
- Chemical to Electrical
- 2 electrodes (anode + cathode), wires connecting them, an electrolyte
44
What is an electrolyte?
Something that conducts electricity when melted or dissolved (e.g. acid/salt solutions)
45
What makes good electrodes?
One anode and one cathode (cannot be same or the cell doesn't work)
46
Anode vs Cathode vs Anion vs Cation
- Anion -, Cation +
- Cathode -, Anion +
- Reversed (since cations go to the cathode and vice versa, but on paper its opposite due to law of charges)
47
Primary cells vs Secondary cells
Primary cells are one time use after oxidation, while secondary cells can be reused by "charging" (reversing reactoin)
48
Dry vs wet cells
Paste/Powder vs liquid electrolyte
49
What is more common nowadays, dry or wet, primary or secondary?
(Evolution)
Dry; Only lead acid is the textbook wet (bottle batteries not used anymore)
Secondary; Primary is not efficient
50
Types of cells
Textbook page 305
51
How did Hans Oersted find the relationship between magnetism and electricity?
He put a circuit next to a compass and the compass moved
52
What is an electromagnet, how is it used, and what are its advantages/disadvantages?
- Conversion: Electricity to Magnetism
- An iron core wrapped by a coil of wire (solenoid)
- Creates a magnetic field when electric current runs through
- Polarity of the magnet can be reversed if current reversed
- A: Powerful, controllable
- D: Lots of energy required, dangerous
53
What did Michael Faraday contribute to the field of electromagnetism?
He introduced many of the basic terms (e.g. anion, cation, ion, electrode, anode, cathode, etc.) and discovered basic principles
54
How do you induct voltage and current into a wire (with or without a load) using a magnet?
- Conversion: Magnetism to electricity
- Move the wire or magnet at an angle relative to each other
55
How do you make an electromagnet stronger?
1. Increase number of coils
2. Make core larger
3. Increase the current
56
What is an electric generator?
Anything that converts motion (mechanical energy) into electricity
57
What is an electric motor?
Anything that converts electricity into motion (mechanical energy)
58
Fleming's rules description
(Motor-Left, Generator-Right: MLGR or Minecraft MLG, R)
- Thumb, index and middle fingers perpendicular
- Thumb = Motion of armature, Index = Magnetic field (N>S), Middle = Current (+>-)
- Left: Trying to find motion
- Right: Trying to find current
- Whichever hand you are using, the same side conductor will represent the current
*DO NOT FORGET TO SWITCH HANDS*
59
How does a DC generator work, and what is its alternate name?
ALTERNATE NAME: Dynamos
- Since every half rotation the armature switches polarity, we need the brushes to switch contact to negate this switch. To make the switching more smooth, we add a split-ring commutator (metal).
An external force turns the armature windings, and when it turns, it cuts the "field lines", generating an electric current, which is then used by the load.
In a dynamo, the "switch" occurs in the armature windings, and the current direction in the external circuit is unaffected.
60
How does the split-ring commutator work?
The split-ring commutator is a piece of metal (or 2 pieces depends) with an insulator to act as a gap. The gap is for the two brushes' currents to not intersect with each other. Otherwise, it is just to make the switch in contact (brush + armature ends) more smooth.
61
What are the parts of a dynamo?
- Stator (non-moving): 2 Field magnets which provide magnetic fields
- Rotor (moving): Armature coil
- Brushes
- Load
(Above will be the same for all 4, but the bottom decides difference)
- 1. Motor or Handle (shaft) that provides mechanical force
- 2. Split-ring commutator
62
How does an AC generator work?
Shaft/External force provides mechanical energy, which moves the armature, cutting the field lines, which creates a current. Each half turn, the polarity reverses and so does the direction of the current. The reversing process is shown in the external circuit this time, not the armature, contrasting the dynamo.
63
What are the parts of an AC generator?
- Rotor (Armature windings)
- Stator (field magnets)
- Brushes
- Load
- 1. Shaft/Handle
- 2. Slip Rings (S1, S2)
64
How do slip rings work and how are they different from split-rings?
Slip rings are not split apart and only transfer current between the brushes and the armature.
65
How does a DC motor work?
When the source provides electricity to the armature, the armature itself becomes an electromagnet. The two magnetic fields repel and attract each other, which moves the armature. The armature is energized until brushes reach the gaps, and the armature uses inertia to lapse the "dead zone". Then, the brushes switch contact and the armature keeps moving. Adding more coils will make the force (torque) more consistent, and will decrease the "dead zone" time.
- "Switching" occurs in armature
66
Parts of a DC motor?
- Rotor
- Stator
- Brushes
- 1. Source + Terminals
- 2. Split-ring Commutator
67
How does an AC motor work?
A source of electricity is provided to the stator (laminated sheets of metal with coils in the grooves), generating a moving magnetic field. The magnetic flux energizes the rotor, and the rotor also starts spinning, and receives an extra boost from the other magnetic field. After this initial induction, as long as the stator is being charged, the rotor is moving at high speed.
68
Parts of an AC motor?
- Rotor (Electromagnet with core)
- Stator (Field magnets replaced with electromagnet composed of core (stack of metal discs with slots + coils/windings occupy the slots)
- Brushes
1. Source + Terminals
2. NO SLIP RINGS
(This is due to AC motors creating a rotating magnetic field with the stator, so you just have to power the stator and no need for rings)
69
Why do most power plants use AC generators?
AC electricity can go for longer distances, and lose less energy along the way (more efficient), and it is easier to change the voltage
70
What are transformers?
Devices that increase or decrease voltage for easier and safer transportation of electric current
(Step up and step down)
71
What is the Canadian household's normal voltage(s)?
240V/120V
240: Large appliances like stove, oven, dryers, water heaters, AC, etc.
120: Small appliances like household lighting, devices, outlets, microwaves
72
How do thermoelectric generators work?
Combustion of fuel (biomass, coal, oil, etc.) creates steam filled with internal energy. This internal energy is converted to mechanical energy when turning a turbine, and the turbine is the shaft of an electromagnetic generator, which produces electricity.
73
What is the difference between sustainable, renewable and non-renewable resources?
Sustainable: Can be continue to be used, but must allow resource to self-replenish at its required speed (slow down exploit)
Renewable: Can be almost infinitely used
Non-Renewable: Cannot be infinitely used, replenishing either impossible or too slow to be considered sustainable
74
What is open-pit mining?
Mining out of a big pit. It disturbs the ecosystem heavily.
75
What are the three direct, primary impacts of using fossil fuels?
Tailing ponds (Toxic waste) (can be filtered), acid rain (SO2) (scrubbers remove) , global greenhouse effect (CO2) (nothing removes)
76
What are tailing ponds?
Ponds severely contaminated by waste from mining sites; Water had been seeped into
77
What is the most common fuel for thermoelectric power plants?
Coal
78
What do scrubbers and electrostatic precipitators do?
Scrubbers remove SO2 while electrostatic precipitators remove solid particles (Both remove harmful waste from the smokestack emissions) by spraying then reacting with it
79
What are greenhouse gases?
Any gas that traps heat in the atmosphere/earth
80
Pros/Cons of thermoelectric plants
Pros:
- Efficient
- Abundant
Cons:
- Lots of pollution
- Non-renewable resource (mostly use coal, biomass has pollution)
- Disturbs natural habitats and changes environment drastically
81
How do hydroelectric plants work?
Dams block water, which builds up pressure, and under the penstock the pressurized water flows down to the generator which spins the turbine and activates the generator, producing electricity
82
Pros/Cons of hydroelectric dams
Pros:
- Efficient
- Non-polluting
- Renewable and abundant
Cons:
- Dangerous (floods)
- Expensive to build
- Destroys habitats (create reservoir around dam)
83
How does a nuclear plant work?
Bomb uranium with neutrons so that nuclear fission occurs (releasing pure energy (gamma), high speed electrons/positrons (beta), and helium with no electrons (alpha)), giving large amounts of energy. This energy is used in a thermoelectric generator.
84
What is the foreseeable future for nuclear generators?
We could use nuclear fusion instead of fission, which produces much more energy and does not excrete waste
85
What are the pros/cons of nuclear generators?
Pros:
- Efficient
- Abundant
- Powerful
Cons:
- Extremely dangerous
- Radiation
- Nuclear waste
86
What is thermal pollution?
The artificial change in temperature of a water body, which degrades its quality for life to survive in it (e.g. hot waste heats the water, organisms extirpated in that area)
87
What is cogeneration, and what are cogeneration systems?
Uses waste from one generator as fuel from another, these generators from a system where e.g. both heat and electricity are generated and used appropriately
88
What are some alternative power sources?
- Wind turbines (reliant on wind existence)
- Solar power (Less sun = no energy)
- Solar farms (reflective mirrors)
(DOES NOT USE SOLAR PANELS), only heat a liquid which is used in a thermoelectric generator
- Tidal energy (cannot be used in most places in the world)
- Geothermal (Expensive and not many places are suitable)
89
What is a transformer and how does it work, how to differentiate between step-up and step-down?
- A transformer is an iron square with coils wrapped on two sides.
- The entering side is an electromagnet.
Energizing input coil creates a magnetic field which gives the output coil voltage.
- Degree of the magnetic field and voltage affected with how many coils you use
- A step-up has less coils on enter than output, and step-down has more coils on enter than output.
> down
< up
90
How does electricity from the generating station get to our homes?
Station, transformer, transmission lines, house
91
Within our homes, what is the route of the electricity from the generating stations?
Electricity meter, breaker panel / fuse box, appliances
92
What does an electricity meter do, what is it and how do you read it?
A meter that records how much electricity you are using (utility bills). Each dial represents a digit, and you look to the lower (even if the hand exactly on number), first digit on right-most side
93
What does the circuit breaker/fuse box do and how do they differ?
They both act as safety measures that break the current if there is danger. The circuit breaker can be used many times by simply flipping the switch (bimetallic strip heats up, bends, lets go, current dislocates), but fuse box melts the fuse and you have to replace it. Fuse boxes are normally used in old homes.
94
What are branch circuits?
Circuits that connect the electricity from the service panel to all across your home (current increases as # parallel routes increases)
- Each has a branch breaker
95
What are the 3 parts of an electric cable?
Black = hot wire, White = neutral wire, copper/green = ground wire
96
What is the electrical code?
A set of standards needed to be met by electricians after wiring a house (strict regulations for safety)
97
How do digital circuit boards work?
Millions of electronic switches act like binary code to program circuit board functions
98
What is the binary code?
A string of 0's and 1's to resemble a code (e.g. binary 11 = 4). 0 = off, 1 = on
99
What processes logical binary information?
Logic circuits
100
What do modern digital devices use in their circuit boards for binary code representation?
Transistors (rheostats)
101
What is power, and its general description of the concept? What are some common units that are used related to power?
Power is the rate of energy consumption/conversion (per unit time). Its unit is the watt, which is joules per unit second. One unit that contains the watt is kWh, though it is not a power unit but an energy unit.
102
What are the Energuide labels for?
They help you compare appliances' energy usage by showing its kWh consummation per year (Regulated by the CSA or Canadian Standards Association)
103
How to calculate electric efficiency?
( Used energy (output) / Total energy (input) ) x 100%
104
What are incandescent lightbulbs and how efficient are they?
They are lightbulbs which light up by heating a tungsten filament; Not efficient, only 5%
105
What are halogen bulbs and how efficient are they? What hazards do they have?
They use pressured-up gases with traces of iodine (prevents evaporating filament). These gases allow for higher temperatures and efficiency; 15%. This bulb risks fire hazards, but can last 2-6 times longer than incandescent bulbs.
106
What are fluorescent tubes and how efficient are they?
Filled with mercury and glow when electrodes are energized. They last 10-13 times longer than incandescent bulbs and are about 20% efficient.
107
Which kills: Current or Voltage?
Current; even 1A, the unit would kill you many times over. If hit in a critical area, even 0.002A can kill (2mA)
108
How to make electricity safe indoors?
- Do not plug in too many cables
- Replace frayed cords
- Do not let water be around cables
- Use receptacle covers
- Do not fix/work on/clean appliances that are still plugged
109
How to make electricity safe outdoors?
- Do not touch live cables/wires
- Do not use ungrounded or frayed 2 prong cables outdoors
- Do not operate while raining
- Before digging, make sure there are no cables under
110
What is a short circuit?
A closed circuit without a significant load; Current becomes too high and fires are prone to start
