الفيزياء للصف الثالث الثانوى 2022 - الفصل الرابع- المعاوقة الكهربية

Introduction

This tutorial provides a comprehensive guide on electric resistance, as discussed in the video by Mr. Hossam Khalil. Understanding electric resistance is crucial for high school physics students, particularly those preparing for their third secondary exam. This guide will break down the concepts, calculations, and applications related to electric resistance.

Step 1: Understanding Electric Resistance

• Definition: Electric resistance is the measure of the opposition to the flow of electric current in a conductor.
• Formula: The resistance (R) can be calculated using Ohm's law: [ R = \frac{V}{I} ] where:
  • R is the resistance in ohms (Ω)
  • V is the voltage in volts (V)
  • I is the current in amperes (A)

Step 2: Factors Affecting Resistance

• Material: Different materials have different resistivities. Conductors (like copper) have low resistance, while insulators (like rubber) have high resistance.
• Length of Conductor: Resistance increases with the length of the conductor. Longer wires have more resistance.
• Cross-Sectional Area: Resistance decreases as the cross-sectional area increases. Thicker wires allow more current to pass through.
• Temperature: Resistance typically increases with temperature for most materials.

Step 3: Series and Parallel Circuits

• Series Circuits

  • Total Resistance (R_total) is the sum of individual resistances: [ R_{total} = R_1 + R_2 + R_3 + \ldots ]
  • Current remains the same through each component.

• Parallel Circuits

  • Total Resistance can be calculated using: [ \frac{1}{R_{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3} + \ldots ]
  • Voltage remains the same across each branch, while current can vary.

Step 4: Practical Applications of Resistance

• Electrical Devices: Understanding resistance is essential for designing circuits in everyday devices like light bulbs and heaters.
• Safety: Knowledge of resistance helps in understanding how to avoid overheating in electrical systems.
• Electronics: Resistance plays a crucial role in signal processing and circuit design.

Step 5: Solving Resistance Problems

• Example Problem: Calculate the total resistance in a series circuit with three resistors: 4Ω, 5Ω, and 6Ω.
  • Calculation: [ R_{total} = 4Ω + 5Ω + 6Ω = 15Ω ]

Conclusion

In this tutorial, we covered the fundamental concepts of electric resistance, including its definition, influencing factors, circuit types, and practical applications. Understanding these principles is essential for mastering physics concepts related to electricity. For further study, practice solving resistance problems and explore more advanced topics related to electrical circuits.