Obj 1 = identify DC, AC, electrolysis, electromagnetism
Generator: has stator with magnets and rotor with many wires wrapped around it that spins.
Step down transformers reduce power line high voltage to low voltage for your house. This transformer is usually for the district of your home.
homes usually supplied with 240v, some appliances are 120v. Both voltage available in distribution panel.
A class 2 transformer is used in HVAC (converts 120vac to 24vac)
Electron Theory
Matter
All forms of matter exist in the state we are familiar with is due to the amount of heat and pressure contained.
Element
periodic table lists various known elements.
Matter with more than 1 element is a compound. Water is a compound, copper is an element.
Molecule
smallest particle that can exist and still exhibit characteristics of the original material.
Smallest part that can be observed before you are breaking up into atoms.
a compound can be broken down into elements or molecules
Atoms
Smallest particles that can exist that can still exhibit characteristics of that element.
Can actually be broken down into smaller constituents (protons, neutrons, electrons) with its Nucleus and electrons orbiting it like the sun
Nucleus holds protons and neutrons
electrons orbit the nucleus. Due to the magnetic attraction from the charge of the protons.
Charge determined by # electrons orbiting nucleus compared to protons
negative if more electrons, positive if more protons
May have more than 1 shell of electrons orbiting, the further away the electron is, the easier it is for that electron to get knocked out of the shell to share with a different atom - this is what a conductor is.
Current
Defined as electron flow
1 ampere = 1 coulomb per second (easier way to measure electron flow) = 6.28 × 10^18 electrons
Capital letter I represents current (coulomb is hard to abbreviate)
Voltage
imbalance of electron distribution or a charge difference between 2 points
Difference in charge
Measured in volts, abbreviated letter E
“Electrical Pressure” that must exist in order for current to flow.
Aka Electromotive Force
More voltage applied on the same resistance = more current flow (V=IR)
Electrical fire may happen if components cannot sustain the higher current flow (which may happen it overvoltage). This is due to heat.
6 ways to produce:
Magnetic - alternator or generator
Chemical - reaction between 2 substances (battery)
Friction - static charge from rubbing 2 materials together
Heat - 2 dissimilar metals joined at a junction (thermoplie or thermocouple), when heat detected there is a voltage formed from that junction.
Pressure - piezoelectric effect when pressure applied to a crystal (barbecue igniters)
Light - light striking photovoltaic or solar cells
Resistance
low resistance = conductor, high = insulator
Opposition to current flow
Abbreviation is R
Messured in ohms
Alternating current
electrical current generated by power plants is commonly AC
usually 3600 rpm
To get 60hz, generators use many wires electrically insulated to pass through magnetic field in one second.
Usually 3 phase to allow smaller conductors to be used.
As a rotor spins, north pole wires get a negative charge and south pole gets a positive charge, as the rotor spins, the wires lose their charge and come around to the next magnet pole, alternating the charge.
Direct current
always same direction
Electron flow in a battery is from negative to positive terminal. Continues until there is no charge differences between battery poles
when recharging, electron flow is reversed which restores battery poles
Electrolysis
break down ionic compounds into their elements
Electrolyte = solution often with water mixed with a compound (results in a mixture of positive or negative charge when mixed).
Each part of the compound has ions with a negative or positive charge.
Electrolysis needs electrical energy to drive the reaction, this is applied to the 2 terminals:
In electrolysis, the anode is positive and cathode is negative (anode is oxidized always, cathode is reduced always) [oxidation is losing electrons, reductions is gaining electrons]
Electroplating is an example, where the product is coated by using the base metal as a cathode
Electrolysis can be destructive in piping systems, it can cause corrosion. Minimized by using alternate materials or sacrificial anode.
Electromagnetism
When current flows through conductor, magnetic field is generated. Strength of this field is directly proportional to how much current is flowing.
A magnetic compass would point parallel to the magnetic field set up around the wire (not point to the wire). It follows the magnetic lines of flux.
Essentially it would make a perpendicular line with the wire if you holding it above the wire with it was live.
If held to the right side, it the compass needle would point up and down
Electromagnet is several turns of wire wrapped around an iron core.
Strength of magnetic field dependent on:
type of core material
amount of current passing
number of turns of wire around core.
Great advantage of electromagnets is that you control when they are magnetic, if no current, then there is no magnetic field.
Transformer:
Induced voltage only happens when current is changing (AC circuits)
mutually induced voltage via iron core between 2 coils. Amount of voltage depends on coil turns. Less coils on secondary means a step down in voltage. Vice versa with more coils.
Obj 2 - Series and parallel circuits
-Series circuit is the simplest. Any fault components in that circuit stops flow.
-Parallel allows multiple paths for current flow
-Series-parallel is 2 series circuits wired together sharing a common power source.
Obj 3- Apply ohm’s law
E=IR : it takes 1 volt to push 1 amp through 1 ohm.
Series: add resistors together for total resistance, voltage is ratio’d by resistance, current is the same
Parallel: 1/RT = 1/R1 + 1/R2 + 1/R3, voltage in parallel is the same but current splits based on ratio.
the total resistance ends up being always less than the smallest resistor in the circuit.