Unit 1: Basic Electricity Principles

1. Voltage, Current, Resistance, and Power

Voltage (V)

Voltage (also called Electric Potential Difference) is the electrical "pressure" that pushes electric charge (current) through a circuit. It represents the work done per unit charge.

Unit: Volt (V).

Current (I)

Current is the rate of flow of electric charge. It is the amount of charge that passes a point in a given time.

Unit: Ampere (A).

Resistance (R)

Resistance is the opposition to the flow of electric current. It converts electrical energy into heat.

Unit: Ohm (Ω).

Power (P)

Electrical Power is the rate at which electrical energy is used or converted.

Formulas:

• P = V × I (Power = Voltage × Current)
• P = I² × R
• P = V² / R

Unit: Watt (W).

2. Ohm's Law

Ohm's Law states that the current (I) flowing through a conductor is directly proportional to the voltage (V) across it, assuming constant temperature.

Formula: V = I × R

This is the fundamental relationship between the three basic quantities.

3. Series, Parallel, and Series-Parallel Combinations

Resistances

• Series: Resistors are connected end-to-end.
  • The current (I) is the same through all components.
  • The total voltage (V) is the sum of individual voltages.
  • Equivalent Resistance (R_eq): R_eq = R₁ + R₂ + ...
• Parallel: Resistors are connected across the same two points.
  • The voltage (V) is the same across all components.
  • The total current (I) is the sum of individual currents.
  • Equivalent Resistance (R_eq): 1/R_eq = 1/R₁ + 1/R₂ + ...
• Series-Parallel: The circuit is a mix of both. To solve, you simplify the circuit step-by-step, combining the simple series or parallel sections first.

Voltages (Batteries)

• Series: Voltages add up. Connecting two 1.5V batteries in series (+ to -) gives 3.0V.
• Parallel: Voltages are the same. Connecting two 1.5V batteries in parallel (all + together, all - together) still gives 1.5V, but doubles the current capacity. (Warning: Only connect identical batteries in parallel).

[Image of series vs parallel resistor circuits]

4. KCL & KVL

These laws are used to analyze complex circuits where simple series/parallel rules don't apply.

Kirchhoff's Current Law (KCL)

Statement: The algebraic sum of all currents entering a junction (or node) is zero.
In simple terms: Σ I_in = Σ I_out
This is a statement of the conservation of charge.

Kirchhoff's Voltage Law (KVL)

Statement: The algebraic sum of all voltages (rises and drops) around any closed loop in a circuit is zero.
In simple terms: Σ V_rises (like batteries) = Σ V_drops (like resistors)
This is a statement of the conservation of energy.

5. AC and DC Electricity

DC (Direct Current)

• Definition: The flow of electric charge is in one direction only.
• Source: Batteries, solar cells, DC generators.
• Waveform: A straight, flat line.

AC (Alternating Current)

• Definition: The flow of electric charge periodically reverses direction.
• Source: Power plant generators (alternators), household wall sockets.
• Waveform: A sine wave (sinusoidal).

[Image of AC waveform vs DC waveform]

6. Electrical Load and its Types

An electrical load is any device that consumes electrical power and converts it into another form of energy (heat, light, motion, etc.).

Types of Loads:

1. Resistive Load:
   • Converts electrical energy to heat.
   • Current and voltage are in phase.
   • Examples: Incandescent light bulbs, electric heaters, toasters.
2. Inductive Load:
   • Uses magnetic fields; stores energy in a magnetic field.
   • Current lags voltage.
   • Examples: Electric motors, fans, transformers, solenoids.
3. Capacitive Load:
   • Stores energy in an electric field.
   • Current leads voltage.
   • Examples: Capacitors, switching power supplies.

7. AC Terminology

Describing an AC sine wave:

[Image of a sine wave labeled with Amplitude, Period, and Cycle]

• Amplitude: The maximum (peak) value of the voltage or current.
• Instantaneous Value: The value of the voltage or current at any specific moment in time.
• Cycle: One complete repetition of the AC waveform (one positive half and one negative half).
• Time Period (T): The time (in seconds) it takes to complete one full cycle.
• Frequency (f): The number of cycles completed per second (f = 1/T).
  Unit: Hertz (Hz). Household electricity is typically 50 Hz or 60 Hz.
• Phase Angle (φ): The angular position of the waveform (in degrees or radians) at a specific instant, often relative to t=0.
• Phase Difference: The angular offset between two different AC waveforms (e.g., the phase difference between voltage and current).