Engineering & Technology

Basic Principles of Electrical Engineering

1. Ohm’s Law

Statement:

$V=$IR

Description: Ohm’s Law relates voltage $\mathrm{<br>}V$V, current I, and resistance R in an electrical circuit. It states that the current through a conductor between two points is directly proportional to the voltage across the two points and inversely proportional to the resistance.

2. Kirchhoff’s Laws

(a) Kirchhoff’s Current Law (KCL)

Statement: The total current entering a junction in a circuit is equal to the total current leaving the junction.

Description: KCL is based on the principle of conservation of electric charge.

(b) Kirchhoff’s Voltage Law (KVL)

Statement: The sum of all the voltages around a closed loop in a circuit is equal to zero. Description: KVL is based on the principle of conservation of energy.

3. Coulomb’s Law

Statement:

$F=k_e\frac{q_1{q}_2}{r^2}F\; =\; k\_e\; \backslash frac\{q\_1\; q\_2\}\{r^2\}$

Description: Coulomb’s Law describes the electrostatic force between two charged particles. The force is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance between them.

4. Faraday’s Law of Electromagnetic Induction

Statement:

$\mathcal{E}=-\frac{d{\mathrm{\Phi }}_B}{dt}\backslash mathcal\{E\}\; =\; –\; \backslash frac\{d\backslash Phi\_B\}\{dt\}$

Description: Faraday’s Law states that a change in magnetic flux through a coil induces an electromotive force (EMF) in the coil. This principle is the basis for electric generators, transformers, and inductors.

5. Lenz’s Law

Statement: The direction of the induced current (or EMF) is such that it opposes the change in magnetic flux that caused it.

Description: Lenz’s Law ensures that energy conservation is maintained in electromagnetic systems.

6. Gauss’s Law

Statement: The total electric flux through a closed surface is equal to the charge enclosed divided by the permittivity of the medium:

${\mathrm{\Phi }}_E=\frac{{\mathrm{Qnec}}_{}}{{\epsilon }_0}\backslash Phi\_E\; =\; \backslash frac\{Q\_\{\backslash text\{enc\}\}\}\{\backslash varepsilon\_0\}$

Description: Gauss’s Law explains the relationship between electric charge and electric field.

7. Conservation of Energy

Statement: Energy can neither be created nor destroyed, only converted from one form to another.

Description: In electrical systems, energy is typically converted between electrical, mechanical, and thermal forms, governed by this principle.

8. Electromagnetic Wave Propagation (Maxwell’s Equations)

Description: Maxwell’s equations describe how electric and magnetic fields propagate and interact. They govern the behavior of electromagnetic waves, which are essential in communication systems, antennas, and waveguides. The four key equations are:

• Gauss’s Law for Electricity
• Gauss’s Law for Magnetism
• Faraday’s Law of Induction
• Ampère’s Law (with Maxwell’s correction)

9. Superposition Principle

Statement: In a linear system, the response caused by two or more stimuli is the sum of the responses that would have been caused by each stimulus individually.

Description: The principle of superposition is used in the analysis of linear circuits to simplify the study of complex circuits with multiple sources.

10. Capacitance and Inductance

(a) Capacitance

Description: Capacitance is the ability of a system to store electric charge. It is defined by the relationship:

$Q=$CV

,where $\mathrm{<br>}C$C is the capacitance, $\mathrm{<br>}Q$Q is the charge, and $\mathrm{<span>V\; is\; the\; voltage.</span>}$

(b) Inductance

Description: Inductance is the ability of a conductor to store energy in the form of a magnetic field when current flows through it. The induced EMF is given by:

$\mathcal{E}=L\frac{dI}{dt}\backslash mathcal\{E\}\; =\; L\; \backslash frac\{dI\}\{dt\}$

$\mathrm{,\; where\; L\; is\; the\; inductance\; and }$$\mathrm{<br>}I$I is the current.

11. Impedance

Description: Impedance is the opposition to the flow of alternating current (AC) and is the combination of resistance, inductive reactance, and capacitive reactance. Impedance is represented as a complex quantity:

$Z=$R+jX

$\mathrm{,\; where\; X\; is\; the\; reactance.<span></span>}$

12. Power in Electrical Circuits

(a) DC Power

$P$=VI

, where P $\mathrm{<span>\; is\; the\; power, </span>}$V is the voltage, and I is the current.

(b) AC Power

In AC circuits, power is divided into:

• Real power $\mathrm{<br>}P$P
• Reactive power Q
• Apparent power $S$S

The power factor plays a key role in determining the efficiency of power transfer in AC systems.

13. Transformers

Description: A transformer transfers electrical energy between two or more circuits through electromagnetic induction. The relationship between primary and secondary voltages is governed by the turn ratio of the transformer.