1. Electrical quantities and their characteristics

LSBU Electrical Circuit Analysis

• EEE_4_ECA

• Professor Mohammad Ghavami

• School of Engineering London South Bank University

• Contact: ghavamim@lsbu.ac.uk

Electrical and Electronic Engineering Overview

• Engineering:

  • Branch of science/technology related to design, development, and building of devices and structures.

• Electrical Engineering:

  • Focuses on systems that utilize electricity; involves higher voltages and power.

• Electronic Engineering:

  • Deals with lower voltages and semiconductor devices.

• Interdisciplinary Nature:

  • Fields converge; examples include electric vehicles, renewable technology, and robotics.

Brief History of Electricity

• 17th Century:

  • Otto von Guericke developed a charge-generating machine.

  • Stephen Gray transmitted electrical charge over long distances.

• Two Charge Types:

  • Charles DuFay identified positive and negative charges.

• Leyden Jar:

  • 1745, van Musschenbroek introduced the first capacitor.

• Franklin's Contributions:

  • Demonstrated lightning as electrical discharge; expanded charge theories.

• Coulomb's Law:

  • 1784: Relationship between charge force and distance established.

• Galvani and Volta:

  • Galvani explored electricity's effects on nerves (1791).

  • Volta created the first voltaic cell (1799).

• Electromagnetism:

  • Oersted announced relationship between magnetism and electricity (1820).

• Transistor and IC Development:

  • 1947: Point-contact transistor.

  • 1958: First integrated circuit developed.

Importance of Electrical Circuit Analysis

• Common Factors:

  • Involves electricity, energy, voltage, and current.

• Interconnections:

  • Related to mechanical engineering and design engineering.

• Challenges:

  • Global warming, energy efficiency, and sustainability drive engineering research.

Systems of Units

• Comparison of English and Metric Systems:

  • Common quantities include length, mass, force, temperature, and energy.

• Prefixes for SI Units:

  • Example: kilo (k), mega (M), giga (G).

Introduction to Electrical Quantities

• Atoms and Structure:

  • Hydrogen atom has a proton and an orbiting electron (negative).

  • Copper is widely used due to its atomic structure with 29 electrons.

Voltage

• Definition:

  • Voltage arises from separation of charges, creating positive ions.

• Coulombs and Charge Definitions:

  • 1 coulomb corresponds to 6.242 x 10^18 electrons.

  • Voltage, V = W/Q, defines potential energy.

Current

• Role of Voltage:

  • Current is the response to applied voltage; charges move through a conductor.

• Ampere Definition:

  • 1 coulomb per second defines current (I).

Voltage Sources

• Types of DC Voltage Sources:

  • Batteries, generators, and power supplies.

• Important Data for Batteries:

  • Ampere-hour (Ah) ratings indicate performance.

Conductors and Insulators

• Conductors:

  • Allow easy electron flow; typically have one valence electron.

• Semiconductors:

  • Equal characteristics between conductors and insulators.

Measurement Instruments

• Ammeters and Voltmeters:

  • Used for measuring current and voltage levels, respectively.

  • Milliammeter and microammeter for smaller currents.

Resistance

• Definition:

  • Resistance opposes charge flow, measured in ohms (Ω).

• Factors Influencing Resistance:

  • Material, length, cross-sectional area, and temperature.

• Formula:

  • R = ρL/A; where ρ is resistivity, L is length, and A is area.

Work, Energy, and Power

• Units:

  • Work/Energy measured in Joules (J).

• Power Definition:

  • Power is rate of energy transfer, P = W/t.

Electrical Energy

• Calculation:

  • E = Pt; Joule is standard unit while kWh is used for large energy amounts.

Graphical Symbols and Units

• Connections and Symbolism:

  • Overview of schematic symbols for electrical components.

• Power Plants and Transformers:

  • Common symbols for electrical machines and devices.

Types of Resistors

• Fixed and Variable Resistors:

  • Overview of different types of resistors and their characteristics.