Fundamental Principles of Electricity and Circuit Analysis

Fundamental Electrical Concepts

Electric Charge: The amount of electrons or protons that possess substance. Measured in Coulombs.

Electricity: A continuous flow or movement of electrons through a material.

Electrical Quantities

• Electric Current: The load carried per unit of time. Formula: I = Q / t. Measured in Amperes (A). Direction: Flows from negative to positive.
• Electromotive Force (EMF): The potential difference between the poles of a generator.
• Electrical Resistivity: The ease or difficulty a material has in allowing electrical current to pass. Measured in Ohms (Ω).

Materials

• Conductors: Materials that allow electricity to flow (e.g., metals like silver and copper).
• Insulators: Materials that block electrical current (e.g., plastics, rubber, gas, dry wood).

Electric Power and Energy

Electric Power: The product of electric intensity and voltage. Formula: P = I × V. Measured in Watts (W).

Energy Calculation: 1 kW·h = 1000 W × 3600s = 3.6 × 10⁶ J.

Ohm's Law

V = I × R | I = V / R | R = V / I

Current Types

• Direct Current (DC): Current that circulates in the same direction. Sources: Car batteries, cells, photovoltaic cells.
• Alternating Current (AC): Current that varies in direction at regular intervals. Sources: Alternators, power grid outlets.

Electrical Circuits

The path of electrical current consists of:

1. Generator: Alternator, dynamo, or battery.
2. Receptor: Resistance, radio, TV, or lamp.
3. Control Elements: Switch or pushbutton.
4. Protection Elements: Fuses.
5. Conductors: Wiring.

Circuit Configurations

• Series Circuit: All circuit elements are traversed by the same intensity.
• Parallel Circuit (Shunt): All elements are connected to the same voltage. The equivalent resistance is smaller than any individual resistor.

Practice Problems

Problem 1: Resistance, Power, and Energy

An electrical resistance of 350 Ω absorbs an intensity of 0.2 A. Calculate the voltage, power, and energy consumed in 8 days and 4 hours.

• Voltage: V = I × R = 0.2 A × 350 Ω = 70 V
• Power: P = I × V = 0.2 A × 70 V = 14 W
• Energy: E = P × t = 14 W × 196 h = 2744 Wh = 2.744 kW·h
• Energy in Joules: 2.744 × 3,600,000 = 9,878,400 J

Problem 2: Calculate Resistance

Calculate the resistance of an apparatus with 144 W power connected to a 12 V voltage.

• Current: I = P / V = 144 W / 12 V = 12 A
• Resistance: R = V / I = 12 V / 12 A = 1 Ω