Kirchhoff’s Voltage Law – Simulator Applet

Kirchhoff's Voltage Law ? Simulator Applet

Updated 20 MAY 2020

Simulator Exercise 02

Name:________________ Section: ____________

I. Purpose. 1. Review the correct use of the Digital Multi-Meter (DMM) for measuring voltage, current, and resistance. 2. Review the application of Ohm's Law in DC series circuits. 3. Introduce the application of Kirchhoff's Voltage Law in the analysis of a DC series circuit. 4. Introduce the calculation of power supplied and dissipated in a DC series circuit.

II. Equipment.

Circuit Simulator Applet An introduction to the Circuit Simulator Applet

III. Pre-lab Calculations. Show all work.

Step One: Calculate total current.

Figure 1

Calculate the total resistance of the circuit RTOT.

Use Ohm's Law to predict the total current in the circuit.

RTOT = _____________

ITOT = _____________

Indicate the direction of total current flow by drawing an arrow and labeling it on Figure 1.

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Kirchhoff's Voltage Law ? Simulator Applet

Step Two: Predict DC voltage values using Ohm's Law.

Use the predicted total current, the nominal value of the resistors, and Ohm's Law to predict the

voltage drop across the 560 ohm and 220 ohm resistors.

V560 = _____________ V220 = _____________

Indicate the polarity of the voltages across the 560- resistor and the 220- resistor on Figure 1.

Step Three: Instructor or lab assistant verification that pre-lab calculations are complete.

______________________________ IV. Lab Procedure. Time Required: 45 minutes. Check-off each step as you complete it. Step One: DC Series Circuit: Measure the resistance of fixed resistors using Ohmmeter. NOTE: When measuring resistance of a component, you MUST ISOLATE the component that you are measuring from the circuit. Figure 2 shows the isolation of a single component with an actual Ohmmeter. Figures 3 and 4 shows how to isolate a single component and measure the resistance using the Ohmmeter in the simulator.

Figure 2: Isolated component

Figure 3: Ohmmeter location in simulator 2 of 9

Kirchhoff's Voltage Law ? Simulator Applet

Figure 4: Isolated component and ohmmeter in the simulator

When measuring total resistance of the circuit, the power source must be removed prior to measuring the resistance. The Ohmmeter will go in the place of the power source. Figure 5 shows the measurement using with an actual Ohmmeter.

780

560 220 Figure 5: Actual ohmmeter connected to measure total resistance

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Kirchhoff's Voltage Law ? Simulator Applet

In the Circuit Simulator Applet, construct the DC series circuit in Figure 1. Use the suggested

layout of Figure 6 to allow easy measurement of current at various points in the circuit.

REMEMBER: The components you need to construct your circuit are located under the Draw tab. You will use the Wire, Resistor, and Voltage Source (2-Terminal) [not to be confused with the A/C Voltage Source].

Figure 6

Measure the total resistance of the circuit as seen by the voltage source.

RT = _____________

State the component that had to be removed and replaced by the Ohmmeter to properly measure

RT.

Component = _____________

Set the DC power supply to 10 volts.

Step Two: Measure DC current. You will measure the DC current in two different places in the DC circuit. To measure the current, you will use an Ammeter. The current that you wish to measure must pass through the Ammeter. To measure this current, you will "open" the circuit and insert the Ammeter. You CANNOT measure current by placing the Ammeter "across" components in the circuit. Figure 7 shows the placement of an actual Ammeter in a circuit.

Figure 7: Actual Ammeter connected to measure current.

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Kirchhoff's Voltage Law ? Simulator Applet

"Open" the circuit between the "+" side of the DC power supply and the 560- resistor. Setup the Ammeter to measure current by connecting it to measure the current through that

opening, as seen in Figure 8.

The green arrow indicates the Ammeter. The Ammeter is found similarly as the Ohmmeter under the Draw/Output and Labels

Figure 8

Record the DC current between the "+" side of DC power supply and 560- resistor.

I = _____________

Remove the Ammeter from the circuit and reinstall the wire connecting the 560- resistor and the power source.

"Open" the circuit between the 560- resistor and the 220- resistor by removing the wire. Connect the Ammeter to measure the DC current through that opening, as seen in Figure 9.

Figure 9

Record the DC current between the 560- resistor and the 220- resistor.

I = _____________

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Kirchhoff's Voltage Law ? Simulator Applet

How closely do the measured current values match? Exact__________ Very close__________ Very Different_________

Why? ______________________________________________________________________________ ____________________________________________________________________________________ How closely do these measured current values match the predicted current value from part one of the pre-lab calculations? If it is not within rounding, then you need to recheck your component settings, measurements or calculations.

Exact__________ Very close__________ Very Different_________

Remove the Ammeter from the circuit and restore the circuit to the setup of Figure 6.

Step Three: Measure DC voltages. For this part we will measure the DC voltage of the power supply and the voltage drops across the 560 and 220 resistors using a Voltmeter. Remember that the Voltmeter leads are placed across the component(s) when measuring the voltage drop across that component. Figure 10 shows the placement of an actual Voltmeter in a circuit.

Figure 10: Actual Voltmeter connected to measure voltage across a component.

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Kirchhoff's Voltage Law ? Simulator Applet

Measure the voltage drop across the 560- and 220- resistors. Ensure that you get proper

polarity indication by putting the "+" sign on the Voltmeter to match the "+" sign you indicated on Figure 1. Setup the Voltmeter to measure voltage by connecting it to measure the across the component, as seen in Figure 11. NOTE: Where you connect the voltmeter to the circuit may vary slightly based on your circuit's node connections.

Node Connection. Properly connected nodes are illustrated with a white dot.

Figure 11

V560 = _____________ V220 = _____________

How closely do the measured DC voltage values match the predicted DC values? Exact__________ Very close__________ Very Different_________

What are possible causes for the differences between the measured and predicted values? ___________________________________________________________________________________ ___________________________________________________________________________________ NOTE: Although the simulation uses an Ohmmeter to measure resistance, a Ammeter to measure current, and a Voltmeter to measure voltage, the actual device used typically will have all three meters in one device. The name of the device is called a Multi-Meter. Since most devices now are digital, you may hear the term in the fleet... Digital Multi-Meter (DMM) which is just another name meter that incorporates the three meters used in this lab in one device.

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Step Four: Verify Kirchhoff's Voltage Law.

On Figure 12, label the DC voltage polarities and the measured DC voltage values of the DC

voltage source, the 560- resistor and the 220- resistor.

Figure 12

Verify Kirchhoff's Voltage Law in this closed loop DC series circuit (calculation required).

Egains = Vdrops ______________ = _______________________=________

How closely does the sum of the DC voltage gains match the sum of the DC voltage drops? Exact__________ Very close__________ Very Different_________

What are possible causes for the differences? ____________________________________________________________________________________ ____________________________________________________________________________________

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