1.2 Fundamental concepts and principles

Electrical engineering revolves around key concepts like voltage, current, and resistance. These form the foundation for understanding how electricity flows and behaves in circuits. Knowing how they relate helps us design and analyze electrical systems.

Power and energy are crucial in electrical engineering, showing how electricity is converted and used. Electric and magnetic fields play a big role too, influencing how charges interact and move. Understanding these basics is essential for tackling more complex electrical problems.

Electrical Quantities

Voltage, Current, and Resistance

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• Voltage represents the potential difference between two points in an electrical circuit
  • Measured in volts (V)
  • Analogous to the pressure difference in a water pipe system
• Current is the flow of electric charge through a conductor
  • Measured in amperes (A)
  • Analogous to the flow rate of water in a pipe
• Resistance is the opposition to the flow of electric current in a material
  • Measured in ohms (Ω)
  • Resistors are components designed to have a specific resistance value (carbon resistors, wire-wound resistors)

Power and Energy

• Power is the rate at which electrical energy is converted into other forms of energy (heat, light, motion)
  • Measured in watts (W)
  • Calculated using the formula: $P = VI$, where $P$ is power, $V$ is voltage, and $I$ is current
• Energy is the capacity to do work and is related to power and time
  • Measured in joules (J) or kilowatt-hours (kWh)
  • Calculated using the formula: $E = Pt$, where $E$ is energy, $P$ is power, and $t$ is time
  • Examples include the energy consumed by a light bulb or an electric motor over a certain period

Electromagnetic Fields

Electric Fields

• An electric field is a region around an electric charge in which it exerts a force on other charges
  • Represented by electric field lines, which point in the direction of the force on a positive test charge
  • The strength of an electric field is measured in volts per meter (V/m)
  • Examples include the electric field between the plates of a capacitor or around a charged particle

Magnetic Fields

• A magnetic field is a region around a magnetic material or moving electric charge in which it exerts a force on other magnetic materials or moving charges
  • Represented by magnetic field lines, which form closed loops and indicate the direction of the magnetic force
  • The strength of a magnetic field is measured in teslas (T) or gauss (G)
  • Examples include the magnetic field around a permanent magnet or a current-carrying wire

Material Properties

Conductors, Insulators, and Semiconductors

• Conductors are materials that allow electric current to flow easily through them
  • Examples include metals like copper, aluminum, and gold
  • Used in wires, cables, and electrical contacts
• Insulators are materials that strongly resist the flow of electric current
  • Examples include rubber, plastic, and ceramic materials
  • Used to prevent current from flowing where it is not desired (wire insulation, circuit board substrates)
• Semiconductors are materials with electrical properties between those of conductors and insulators
  • Examples include silicon and germanium
  • Used to create electronic devices like diodes, transistors, and integrated circuits

Fundamental Laws

Ohm's Law

• Ohm's Law states that the current through a conductor is directly proportional to the voltage across it and inversely proportional to its resistance
  • Mathematically expressed as: $V = IR$, where $V$ is voltage, $I$ is current, and $R$ is resistance
  • Allows for the calculation of voltage, current, or resistance when the other two quantities are known
  • Applies to many electrical components and circuits, such as resistors, wires, and simple devices like light bulbs and heating elements