Notes on Principles of Electricity

System of Units

• SI Units: Le Système International d’Unités, adopted as a standard for scientific and engineering literature.

  • Base Units:

  • Mass: kilogram (kg)

  • Length: meter (m)

  • Time: second (s)

  • Electric Current: ampere (A)

  • Temperature: kelvin (K)

  • Amount of Substance: mole (mol)

  • Luminous Intensity: candela (cd)

Electrical Quantities & Units

• Main electrical quantities and their units:

  • Charge (Q, q): coulomb (C)

  • Current (I, i): ampere (A)

  • Electric Field (ε): volt/meter (V/M)

  • Voltage (V, E, v): volt (V)

  • Resistance (R): ohm (Ω)

  • Conductance (G): siemen (S)

  • Energy (W): kilo-watt-hour / joule (kWh / J)

  • Power (P): watt (W)

  • Time (t): second (s)

  • Frequency (f): hertz (Hz)

  • Radian Frequency (ω): radian/sec (rad/s)

  • Phase Angle (Θ, φ): degree or radian (° or rad)

  • Impedance (Z): ohm (Ω)

  • Admittance (Y): siemen (S)

  • Inductance (L): henry (H)

  • Capacitance (C): farad (F)

  • Magnetic flux (Ф): weber (wb)

  • Magnetic flux density (B): tesla (T)

Metric Prefixes

• Multiplication Factors:

  • 1 E = $10^{18}$

  • 1 P = $10^{15}$

  • 1 T = $10^{12}$

  • 1 G = $10^{9}$

  • 1 M = $10^{6}$

  • 1 k = $10^{3}$

  • 0.001 m = $10^{-3}$

  • 0.000001 µ = $10^{-6}$

  • 0.000000001 n = $10^{-9}$

  • 0.000000000001 p = $10^{-12}$

  • 0.000000000000001 f = $10^{-15}$

  • 0.000000000000000001 a = $10^{-18}$

Atomic Structure of Matter

• Definition: Matter is anything that has mass and occupies space, composed of atoms.

• Atoms:

  • Central nucleus surrounded by electrons.

  • Protons (+) and neutrons (0) in nucleus; electrons (-) orbit the nucleus.

  • Protons and neutrons have mass approximately 1800 times that of electrons.

Conductors, Insulators & Semiconductors

Conductors

• Definition: Materials allowing free passage of current, possessing many charge carriers.

• Examples: All metals, with silver, copper, gold, aluminum, iron as common conductors. Copper is most popular.

Insulators

• Definition: Materials with very low electrical conductivity, preventing current flow.

• Examples: Wood, paper, rubber, glass, mica, ceramic, air. Vacuum is a perfect dielectric.

• Dielectric Strength: Minimum field strength to cause breakdown of an insulator. For example, air has a dielectric strength of 30 kV/cm.

  • Calculation Example: Voltage causing breakdown for air with thickness of 6mm:

  • V = 30 ext{kV/cm} imes 0.6 ext{cm} = 18 ext{kV}

Semiconductors

• Definition: Materials exhibiting electrical conductivity between conductors and insulators; conductivity can be varied by external fields.

• Importance: Foundation of modern electronics (transistors, diodes, etc.).

• Common Materials: Silicon (Si), Germanium (Ge).

Electrical Charges

Static Electricity

• Definition: Electric charges separated by friction in insulating materials.

• Example: Rubbing glass with silk creates positive charge on glass and negative charge on silk.

Behavior of Charges

• Attraction and Repulsion:

  • Unlike charges attract (e.g., positively charged glass rod and negatively charged ebonite rod).

  • Like charges repel (e.g., positively charged glass rods repel each other).

Electrical Potential Difference

Definition

• Electric Potential: Work required to move a unit charge between two points in a circuit.

  • Formula: V = rac{W}{Q} where:

  • V = potential difference (volts)

  • W = energy (joules)

  • Q = charge (coulombs)

• Interpretation of Voltage: One volt is the potential difference where 1 joule is needed to move 1 coulomb of charge.

Electron Flow vs Current Flow

• Historical Convention: Current is assumed to flow from positive to negative, though actual electron flow is from negative to positive.

• Summary: Electrons flow from the negative end of the battery to the positive end, while current flows from the positive end to the negative end.