Principles of Electricity

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:

    1. Magnetic - alternator or generator

    2. Chemical - reaction between 2 substances (battery)

    3. Friction - static charge from rubbing 2 materials together

    4. Heat - 2 dissimilar metals joined at a junction (thermoplie or thermocouple), when heat detected there is a voltage formed from that junction.

    5. Pressure - piezoelectric effect when pressure applied to a crystal (barbecue igniters)

    6. 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:

        1. type of core material

        2. amount of current passing

        3. 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.