Lecture Notes on Basic Concepts and Laws of Electricity

Introduction

• Basic concepts of electricity, familiar from O-level physics.
• Topics covered: electrical charge, conduction in metals, voltage, current, power, energy, resistivity, circuit connections, and culture sports.

Electric Charge

• Fundamental quantity in electric circuits.
• Atoms consist of electrons, protons, and neutrons.
• Charge of Electron: -1.602 x 10^-19 coulombs.
• Coulomb: Large unit, 6.24 x 10^18 electrons per coulomb.
• Laboratory values are usually in microcoulombs, nanocoulombs, or picocoulombs.

Conduction in Metals

• Metals have conductive properties due to valence electrons.
• Metallic Bonds: Electrons shared in a "sea" around positive ions.
• Electric Current: Motion of free electrons when a potential is applied.

Voltage and Current

• Voltage (V): Work needed to move a unit charge between two points.
• Current (I): Charge flow per unit time, measured in amperes (A).
• The flow of electrons creates a current from negative to positive terminals.

Power and Energy

• Power (P): Time rate of energy expenditure, measured in watts (W).
• Energy: Capacity to do work, measured in joules (J).
• Example: 100 W bulb for 2 hours -> 0.72 MJ energy consumed.

Resistivity and Resistance

• Resistivity: Material's opposition to current, depends on material and temperature.
• Resistance (R): Proportional to length, inversely to cross-sectional area.
• Ohm's Law: V = IR, relates voltage, current, and resistance.
• Conductance (G): Reciprocal of resistance, measured in Siemens.

Circuit Analysis

• Nodes: Points of connection between branches.
• Branches: Elements between two nodes.
• Loops: Closed paths in a circuit.
• Kirchhoff’s Laws:
  • Current Law: Sum of currents entering a node equals the sum leaving.
  • Voltage Law: Sum of voltages around a loop equals zero.

Resistors in Circuits

• Series: Equivalent resistance is the sum of resistances.
• Parallel: Reciprocal of equivalent resistance is the sum of reciprocals.
• Voltage Divider Rule: Voltage across a resistor in series is a fraction of total.
• Current Divider Rule: Current through a branch is a fraction of total current.

Practical Examples

• Voltage Drop: Calculating across a transmission line.
• Safety with Electricity: Effects of current on the human body, safe handling of electrical devices.

Conclusion

• Understanding basic laws and concepts is crucial for circuit analysis.
• Emphasis on practice and asking questions to clarify understanding.