# DC Circuits

Simulation Used: Circuit Construction Kit (DC) from the PhET at the University of Colorado.
• Initial settings:
• Select "Voltmeter" and "Ammeter" from the "Tools" menu on the right.
• Select "Schematic" from the "Visuals" menu on the right.

• Activity 1: Determine the current through and the voltage across the resistors in the following circuit.
• Build the circuit shown on the diagram above:
• Click on a resistor and drag it into the circuit board. Repeat for two more resistors.
• Click on the battery and drag it into the circuit board.
• Drag wires and connect the resistors and the battery as shown on the diagram above. Two elements are connected when their ends overlap. To disconnect two elements, right-click on the joint and select "split junction".
• Right-click over each resistor and the battery and change their value to be equal to those shown in the table below.  R1(Ohm) R2(Ohm) R3(Ohm) Voltage (V) 20 40 10 10
• Perform the experiment:
• Using the voltmeter, measure the voltage across each element. Write it down in a table.
• Break the connection between R1 and junction p.A and connect an ammeter. Record the value of the current through R1.
• Break the connection between R2 and junction p.A and connect an ammeter. Record the current through R2.
• Break the connection between R3 and junction p.A and connect an ammeter. Record the current through R3.
• In your lab notebook, write down the data in the following format:

 Resistor Resistance (Ohm) Current (A) Voltage (V) R1 R2 R3

• Results: Is the total current through R1 and R2 equal to that through R3? Is the sum of the voltages across R1 and R3 equal to that of the battery?

• Activity 2: Determine the resistance of an unknown resistor.
• Un-click "Voltmeter" from the "Tools" menu on the right.
• Using three resistors, a light bulb, an ammeter, and a battery, construct the circuit shown above.
• Set the values for R1, R2, R3, and the Battery as:  R1(Ohm) R2(Ohm) R3(Ohm) Voltage (V) 48 16 81 10
• Drag and connect an ammeter between junction points A and B.
• Perform the experiment:
• Repeatedly, right-click and change the resistance of the light bulb until the current through the ammeter is zero.
• Record the value for the resistance of the light bulb.
• Measure the voltage across each resistor and record the values in your notebook.
• In your lab notebooks, write down the data in the following format:

 Resistor Resistance (Ohm) Voltage (V) R1 R2 R3 Lightbulb

• Results: Compare the ratios R1/R2 vs. R3/Rlightbulb. Are they equal? Compare V1 and V3. Are the equal? Compare V2 and Vlightbulb. Are they equal?How much is V1+V2? How much is V3+Vlightbulb?
• Bring your notebook to our next class!

Acknowledgements.
• The Java Applet comes from the PhET Interactive Simulations at the University of Colorado, Boulder.
• Partial Funding for the creation of this lab manual was provided by the VCCS Paul Lee Professional Development Grant Program.