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Resistance and Ohm’s Law

This article explores the concepts of electric resistance and Ohm's Law, which describe how electric charges experience opposition as they move through conductors. It covers the fundamental relationship between voltage, current, and resistance, defined by Georg Ohm, and introduces terms like electrical insulators and conductors. The article also provides practical circuit analysis techniques using Kirchhoff's Laws, including examples of series and parallel circuits. Gain insight into calculating resistance and voltage drops, aiding in the effective analysis of electrical circuits.

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Resistance and Ohm’s Law

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  1. Resistance and Ohm’s Law

  2. When electric charges flow they experience opposition or resistance which reduces the amount of energy they have • Greater resistance -> greater amount of energy each charge has to give up

  3. Filament – high resistance Therefore, lot’s of energy taken from each electron and turned into light Wire – low resistance Therefore, little energy lost – turned mainly into heat

  4. Electric Resistance • The amount of energy (voltage) required to push electrons (current) through a conductor

  5. German Physicist Georg Ohm determined that for a given conductor, the ratio of voltage to current (V/I) is constant • We call this constant resistance (Measured in Ohms - ) = Resistance Constant

  6. Ohm’s Law • Relates voltage, current and resistance • Note: E stands for electric potential (commonly known as voltage)

  7. Electrical Insultator • Prevents the transfer of electric charges • Ex: Air, glass, rubber, paper • Electrical conductor • Low resistance which allows electric charges to flow easily • Ex: copper

  8. Example 1: • A single cell is set-up in a circuit with a switch and a resistor. For the resistor, a voltmeter is set-up and it measures 1.3V and an ammeter is set-up and it measures 3.5A. • Draw the circuit with the correct set-up of a voltmeter and ammeter • Calculate the resistance of the resistor

  9. Example 2: • If a resistor has a resistance of 1000 and the current is 2.0A. What will be the voltage drop across the resistor?

  10. Work • Pg 330 # 1a • Pg 332 # 1, 3-5 • Pg 331 # 5ab,7,8

  11. Circuit Analysis

  12. Types of Circuits • Series • Only one path for current to flow

  13. Types of Circuits • Parallel • More than one path for current to take

  14. Analysis of Circuits • We have four tools we can use to analyze circuits: • Kirchoff’s Current Law (KCL) • Kirchoff’s Voltage Law (KVL) • Ohm’s Law • Equivalent Resistance (Series and Parallel)

  15. Kirchoff’s Current Law (KCL) • At any junction (Point) in the circuit, the current going in equals the current going out • At a point, Iin = Iout • Note: In any series circuit, every point has the same current

  16. Examples

  17. Kirchoff’s Voltage Law (KVL) • In any complete path in a circuit, the sum of voltage rises (sources) is equal to the sum of voltage drops (loads) • For a path, Vrises = Vdrops

  18. Examples

  19. Work • Pg 337 # 1-3 • Pg 343 # 1, 2, 4

  20. Equivalent Resistance • If you have many resistors (or loads) in a circuit, finding the equivalent resistance allows you to replace multiple resistors with a single resistor • This allows easier analysis of circuits

  21. Equivalent Resistance in Series

  22. Equivalent Resistance in Parallel The easiest way to put this formula into a calculator is to use your inverse button (x-1)

  23. Work • Pg 339 # 4-6 • Pg 340 # 7

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