LU6_Kirchhoff's Rules (1)

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Jul 2, 2024

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Name ______________________ Class Section ________ Date _____________ PHY 242 – Laboratory LABORATORY 6: KIRCHHOFF’S RULES Objectives:  build circuits from schematic drawings.  measure the differences in potential and currents in series and parallel combinations of resistors.  demonstrate Kirchhoff’s Rules for electrical circuits. Materials Required: Computer with Excel and access to simulation Circuit Construction Kit : https://phet.colorado.edu/en/simulation/circuit-construction-kit-dc Software Requirements : Windows Macintosh Chromebook Linux iPad Mobile Phone Chrome, Edge Chrome, Safari Chrome Not recommended Safari Not recommended Introduction: Circuits consisting of just one battery and one load resistance are simple to analyze, but they are not often found in practical applications. Usually, circuits have more than two components connected together. There are two basic ways in which to connect more than two circuit components: series and parallel. The defining characteristic of a series circuit is that there is only one path for electrons to flow. The defining characteristic of a parallel circuit is that all components are connected between the same set of electrically common points, therefore they experience the same difference in potential. There are many paths for electrons to flow, but only one voltage across all components. Series and parallel resistor configurations have very different electrical properties. A multi-loop circuit may have more than one battery in different branches of the circuit. A junction (node) in a circuit is a point where at least three circuit paths meet. A branch is a path connecting two junctions (nodes). To analyze such a circuit and to find the currents in all branches of the multi-loop circuit one must use Kirchhoff's rules. a) Kirchhoff's first rule (junction rule): At any junction point in a circuit where the current can divide, the sum of the currents into the junction (node) must equal the sum of the currents out of the junction (this is a consequence of charge conservation). 1

b) Kirchhoff's second rule (loop rule): When any closed-circuit loop is traversed, the algebraic sum of the changes in the potential must equal zero (this is a consequence of conservation of energy). Activity 1: Voltages in Series Circuits 1. Start the Circuit Construction Kit PhET simulation, Lab tab, and explore it. Make sure that you check the Show Current (conventional), Labels , and Values boxes. Hints for the use of various elements of circuit:  Right-click on the circuit element to change a property (e.g. resistance) or to delete it.  Right-click on junctions to disconnect pieces. 2. Build a simple circuit with a battery, wires, and three resistors of different resistances. Connect the three resistors into the series circuit shown below carefully noting which wire is connected to the negative and which is connected to the positive terminal of the battery. Use the sliders (after clicking on the element of circuit) to choose different values for the resistance of resistors and the voltage of the battery. 3. Use the voltmeter to measure the voltages across the individual resistors and then across the combinations of resistors. Be careful to observe the polarity of the leads (red is +, black is -). Record your readings below. R 1 = ¿ R 2 = ¿ R 3 = ¿ R 12 = ¿ R 23 = ¿ R 123 = ¿ V 1 = ¿ V 2 = ¿ V 3 = ¿ V 12 = ¿ V 23 = ¿ V 123 = ¿ 4. According to your data, what is the pattern for how voltage gets distributed in a series circuit with unequal resistances? 5. Is there any relationship between the size of the resistance and the size of the resulting voltage? 2

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