Electrical Units and Formulas

Matter and the States of Matter

• Four traditional states of matter: solid, liquid, gas, plasma.
• Current knowledge: there are 22 known states of matter.
• Elements and atoms:
  • Elements like iron, gold, silver, oxygen are composed of a single type of atom (element).
  • There are 118 known elements.
• Compounds and molecules:
  • Water is a compound with the chemical formula
    $ext{H}_2 ext{O}.$
  • Ammonia is another example, with formula
    $ext{NH}_3.$
  • A molecule is the smallest unit of a compound that retains its properties; molecules like
    $ext{H}<em>2 ext{O}, ext{O}</em>2, ext{N}_2, ext{etc.}$
  • Atoms join to form molecules, which in turn form most objects around us.
• Basic building blocks:
  • Atoms consist of a nucleus (protons and neutrons) with electrons orbiting in shells.
  • The number of protons defines the element (atomic number).
  • The number of electrons can vary (neutral atoms have equal numbers of protons and electrons).
• Nuclei and electrons:
  • Protons carry positive charge; electrons carry negative charge; neutrons are neutral.
  • The electrons in the outer shells (valence electrons) largely determine chemical behavior and conductivity.
• Atmosphere and radiation:
  • The ionosphere and UV/gamma radiation interact with matter; the atmosphere filters some radiation before it reaches Earth's surface.
• Practical aviation relevance:
  • Understanding matter and atomic structure underpins how electricity moves and how materials conduct or insulate in aircraft.

Atomic Structure and Charge

• The Bohr model (planetary model) is used as a conceptual aid:
  • The nucleus contains protons and neutrons.
  • Electrons orbit around the nucleus in shells (not fixed paths in modern physics, but useful for teaching).
  • Two electrons max in the first shell; eight in the second; 18 in the third; shells continue up to seven total shells in heavier elements.
• Electron behavior and charge:
  • Electrons are far lighter than protons and can move relatively easily; their movement constitutes electric current.
  • Ground state (neutral atom): charges balance, net charge = 0.
  • If an atom loses electrons, it becomes positively charged (cation). If it gains electrons, it becomes negatively charged (anion).
  • Ion: a charged atom or molecule (positive or negative).
• Color-coding (teaching aid):
  • Positive charge / absence of electrons: red.
  • Negative charge / excess electrons: blue.
  • Neutral: purple (red + blue mix).
• Electron shells:
  • Each shell can hold a maximum number of electrons: 2 (first shell), 8 (second), 18 (third).
  • The outermost shell is the valence shell; its electrons are valence electrons.
  • When the outermost shell is full, the atom is generally stable and less reactive.
• Standing electricity (static electricity) concept:
  • Rubbing a carpet can transfer electrons and leave you with a charge (carpets are insulators).
  • Your body is a conductor; contact with a metal object (e.g., a doorknob) can equalize charge and cause a shock.
• Conductors vs insulators:
  • Conductors have high electron mobility (loosely bound valence electrons).
  • Insulators have tightly bound valence electrons; they resist electron flow.
  • Example in a wire: copper is a conductor; plastic is an insulator.
• Semiconductors:
  • Have about 4 or 5 valence electrons; silicon is a common example.
  • Can behave as conductors or insulators depending on doping.
• Practical aviation tie-in:
  • Electrical conductivity of materials in aircraft affects wiring, insulation, and safety against unwanted current paths.

Electrical Current: Electron Flow vs Conventional Current

• Electron flow direction:
  • Electrons move from the negative terminal toward the positive terminal in a circuit.
• Conventional current direction:
  • By convention, current is considered to flow from the positive terminal to the negative terminal.
• Circuit basics:
  • A circuit is a closed loop that provides a path for electrons to move from a source to a load and back to the source.
  • A load (e.g., a light bulb) provides resistance, converting electrical energy into light/heat.
• Electrons as charge carriers:
  • Electrons are not consumed; they carry charge and pass from one component to another.
  • A complete circuit requires a conductive path (e.g., copper wire) to allow continuous electron flow.
• Short circuit:
  • A path with little or no resistance between the source terminals causes a large current, producing rapid heating and potential damage.
  • Fuses are used to automatically cut off current if it becomes too high.

Key Circuit Quantities and Units

• Electrical quantity relationships (Ohm’s law and derived quantities):
  • Ohm’s Law:
    $V = IR$
  • Power in a circuit:
    $P = VI = I^2 R = \frac{V^2}{R}$
• Basic units and prefixes:
  • Voltage (V), Current (A, ampere), Resistance (Ω, ohm), Power (W, watt).
  • Prefixes such as mega-, kilo-, milli-, micro- (e.g., 1
    kW = 1000 W; 1
    mA = 10^{-3} A).
• Energy vs power:
  • Power is the rate of energy transfer; energy is power over time.
  • Electrical energy:
    $E = P t$
  • Energy units: kilowatt-hours (kWh) = power in kilowatts × time in hours.
• Battery capacity:
  • Capacity often given in milliamp-hours (mAh) or ampere-hours (Ah):
    $Q = I imes t ag{charge}$
  • Higher capacity means more charge available before recharge.
• Example comparisons:
  • A 120 W bulb: uses about 1 electron per second (as stated in the lecture; this is a teaching analogy rather than a precise physical claim).
  • Energy example: a 110 V outlet delivering 10 A would provide 1000 W, which is 1 kW of power.
  • A device rated at 110 V and 10 A can also be powered at 220 V with 5 A such that the same power is delivered (if the supply and device support it).
• Real-world example: a 1,100 W PSU at 110 V draws about 10 A; at 220 V it would draw about 5 A, keeping power roughly the same:
  $$ P = VI
  ightarrow 110 ext{ V} imes 10 ext{ A} ext{ vs } 220 ext{ V} imes 5 ext{ A} \