03 - Kirchhoffs Laws Using PhysicsAviary

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2020

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Electrical Engineering

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Apr 3, 2024

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Ammeter – connected in series between two resistors Voltmeter – connected in parallel across one resistor SPH3U1 Lesson 3 Electricity KIRCHHOFF’S LAWS LEARNING GOALS Students will:  Describe what happens to currents and voltages around series and parallel circuits.  State Kirchhoff’s Law.  Apply Kirchhoff’s Laws to analyze currents and voltages in circuits. VIDEOS Physicshelp.ca - Kirchoff's Current Law Physicshelp.ca - Kirchoff's Voltage Law Khan Academy - Kirchoff's Current Law – more detail. Khan Academy - Kirchoff's Voltage Law CONDUCTING AN EXPLORATION – KIRCHHOFF’S LAWS Purpose: To determine the laws that govern current and voltage in series and parallel circuits. Go to the Physics Aviary website. link: http://www.thephysicsaviary.com/Physics/Programs/Labs/find.php SERIES CIRCUIT Scroll down the page to Series Circuits and click on the image to run it. (Or, just click on http://www.thephysicsaviary.com/Physics/Programs/Labs/SeriesCircuitLab/ ) Click Begin . TOTAL VOLTAGE  Click on the Battery Box. Count how many cells are in it. Each cell provides 1.5 V of potential difference. For example, if there are 4 cells, then the voltage of the battery box is 4 x 1.5 V = 6.0 V.  Record your total voltage: ______ cells x 1.5 V = _________.  Click on See Full Circuit. CURRENTS AND VOLTAGES 1

SPH3U1 Lesson 3 Electricity  Click on the ammeter and record the current. Like in a real meter, the value will fluctuate slightly. Record the most frequent value.  Click on the voltmeter and record that value as well.  Click Move Meters and record current and voltage for the other two resistors. Record your results: Current entering: First Resistor: _____ Second Resistor: _____ Third Resistor: _____ Voltage across: First Resistor: _____ Second Resistor: _____ Third Resistor: _____ What conclusions can you draw about current and voltage in series circuits from the from the experiment? Current: Voltage: PARALLEL CIRCUIT Scroll back up the page to Parallel Circuits and click on the image to run it. (Or, just click on http://www.thephysicsaviary.com/Physics/Programs/Labs/ParallelCircuitLab/ ) Click Begin . TOTAL VOLTAGE  Click on the Battery Box. Count how many cells are in it. Each cell provides 1.5 V of potential difference. For example, if there are 4 cells, then the voltage of the battery box is 4 x 1.5 V = 6.0 V.  Record your total voltage: ______ cells x 1.5 V = _________.  Click on See Full Circuit. CURRENTS AND VOLTAGES  Click on the ammeter of the first resistor and record the current. Like in a real meter, the value will fluctuate slightly. Record the most frequent value. Click the ammeter again to 2

SPH3U1 Lesson 3 Electricity return to the circuit. DO NOT USE THE BACK BUTTON OF YOUR BROWSER. DOING THAT WILL FORCE YOU TO CLICK BEGIN AGAIN AND YOU WILL GET A WHOLE NEW CIRCUIT AND HAVE TO START OVER.  Click on the voltmeter and record that value as well.  Click on the meters for the other resistors as well as the ammeter for the battery box to record those values as well. Record your results: Current entering: First Resistor: _____ Second Resistor: _____ Third Resistor: _____ Current Leaving Battery: _____ Voltage across: First Resistor: _____ Second Resistor: _____ Third Resistor: _____ What conclusions can you draw about current and voltage in series circuits from the from the experiment? Current: Voltage: WHAT YOUR RESULTS MEAN Your results are specific results for simple circuits that are connected ONLY in series or ONLY in parallel. In circuits where elements are connected with a variety of connections, we have general laws that govern ALL cases. These were first determined by Gustav Kirchhoff and are named after him. It is this final form of Kirchhoff’s Laws that we will use to analyze circuits in a later lesson. Explain how these statements say the same thing as the results you stated in your experiment. Go back to your circuits and see if these statements are true (of course they are, but you can confirm it). 3 Kirchhoff’s Voltage Law Around any single complete path through an electric circuit, the sum of the increases in electric potential (voltage rise) is equal to the sum of the decreases in electric potential (voltage drop). Kirchhoff’s Current Law At any junction point (i.e. branch point or intersection) in an electric circuit, the total electric current into the junction is equal to the total electric current out (duh… obviously).

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SPH3U1 Lesson 3 Electricity PROBLEMS Find the missing voltages and currents HOMEWORK Read p559-561 in your textbook. 4 V 1 = 6V I 1 = ? I 0 = I 1 = I 3 = V 3 = V 0 = 24V I 0 = ? V 2 = 9V I 2 = 5A V 3 = ? I 3 = ? M I 2 = 4A I 6 = ? I 5 = ? I 4 = 2A I 1 = ? V 3 = ? M I 1 = I 2 = V 2 = I 3 = V 3 = I 4 = V 4 = I 5 = I 3 = ? V 0 = 9V I 0 = 6A V 4 = ? V 1 =4.5V V 2 = ?