CH1_ basic electricity

Chapter 1: Basic Electricity

Introduction

Understanding basic electricity is fundamentally crucial for applications in cathodic protection technology, which is essential for preventing corrosion in various materials, especially metals. Corrosion and cathodic protection are electrochemical phenomena that necessitate a solid foundation in electrical terminology, laws governing electricity, and the principles of circuits.

1.1 Electrical Terms

1.1.1 Electrons

• Electrons: Negatively charged subatomic particles that play a key role in forming chemical bonds and holding matter together, akin to mortar in a brick wall.

1.1.1.1 Voltage (V)

• Voltage: Refers to electromotive force or electric potential difference, fundamentally driving the flow of electric current. It is measured in volts (V), millivolts (mV), and microvolts (μV).

• Relationship: 1 kilovolt (kV) equals 1,000 volts; 1 volt equals 1,000 millivolts; and 1 millivolt equals 0.001 volts.

• Common Symbols and Abbreviations:

  • emf – electromagnetic force

  • E or e – represents voltage across a source

  • V – represents voltage across a sink

1.1.1.2 Current (I)

• Current: The flow of charged particles through a conductor, which is measured in amperes (A), milliamperes (mA), and microamperes (μA).

• Symbols:

  • I = current

  • A = amperes

  • mA = milliamperes

  • μA = microamperes

• Flow Rate: 1 ampere corresponds to a flow rate of 1 coulomb per second (1 coulomb ≈ 6.242 x 10^18 electrons).

1.1.1.3 Resistance (R) and Resistivity (ρ)

• Resistance: Represents the opposition to the flow of electric charge in materials; measured in ohms (Ω).

• Resistivity: A material property that quantifies how strongly a given material opposes the flow of electric current, measured in ohm-centimeters (Ω-cm).

• Resistance Relationship Formula:[ \rho = \frac{R \times A}{L} ]where ( R ) = resistance, ( A ) = cross-sectional area, and ( L ) = length of conductors.

1.1.1.4 Electrical Schematic Diagram Symbols

• Common components encountered in schematic diagrams include:

  • Resistor

  • Ground symbol

  • Battery

  • Electrical connection

  • Rectifier

  • Switch

  • Diode.

1.1.2 Electrical Laws

1.1.2.1 Ohm's Law

• Ohm's Law: Defines the relationship between voltage (E), current (I), and resistance (R):[ E = I \times R ]

• This law can be rearranged based on what quantity is unknown, giving: [ I = \frac{E}{R} ] and [ R = \frac{E}{I} ].

• Ohm's Law Triangle:

  • E (Voltage)

  • I (Current)

  • R (Resistance).

1.1.2.2 Power (P)

• Power: Represents the rate at which electrical energy is consumed or converted, measured in watts (W).

• Power Equations:[ P = E \times I ][ P = I^2 \times R ]

• Understanding these equations is crucial for electrical system design and energy efficiency measurements.

1.1.2.3 Kirchhoff's Laws

1.1.2.3.1 Voltage Law

• Voltage Law (KVL): States that the total sum of voltages in a closed circuit loop is equal to the sum of the voltage drops across the resistances in that loop.

1.1.2.3.2 Current Law

• Current Law (KCL): Asserts that the total current entering a junction must equal the total current leaving the junction, emphasizing conservation of electric charge.

1.1.3 Circuits

1.1.3.1 Series Circuit

• Series Circuit: A circuit configuration where components are arranged in a single path; thus, current is uniform throughout all components, though the voltage drop across each component can vary.

1.1.3.2 Parallel Circuit

• Parallel Circuit: A configuration wherein components are connected across the same two points; the voltage across each component remains constant, while the current can differ among them.

1.1.3.3 Series-Parallel Circuit

• Series-Parallel Circuit: Combines characteristics of both series and parallel circuits, creating complex electrical configurations that are frequently encountered in practical applications.

1.1.2.8 Direct and Alternating Current

• Direct Current (DC): Electric current that invariably flows in one direction, making it easy to visualize as a straight line on an oscilloscope graph.

• Alternating Current (AC): Current that periodically reverses its direction, represented by a sinusoidal wave pattern on an oscilloscope; it is the primary form of electricity supplied to homes.

• Transformers: Devices used to adjust the voltage level of AC through electromagnetic induction, allowing efficient energy transmission over long distances.

1.1.2.9 Meter Operation

• Analog Meters: Utilize electromechanical mechanisms, such as a needle and scale, to display readings, which can be subject to calibration and mechanical errors.

• Digital Meters: Employ electronic components to provide numerical displays, offering enhanced accuracy and ease of reading.

• Functionality for Measuring:

  • Voltage (V): Connected across a circuit element (high resistance) to measure voltage without significantly affecting the circuit.

  • Current (A): Requires the meter to be connected in series (low resistance) to accurately measure the flow of current.

  • Resistance (Ω): Measured by connecting across a circuit element utilizing the meter's internal voltage source.

Exercises

Practical exercises include applications of Ohm's Law, determining voltage drops, performing current calculations, and real-world measurements to enhance understanding of circuit behavior.

Appendix

Includes a guide on interpreting resistor color codes and instructions for the proper maintenance and use of various types of meters, crucial for effective troubleshooting and diagnostics in electrical circuits.