Circuit Lab

DC Circuit Simulation Lab

Download Circuit Construction Kit at:

http://phet.colorado.edu/new/simulations/sims.php?sim=Circuit_Construction_Kit_DC_Only

Learning how to use the program

The left hand (sky blue) panel, is the playing surface.

The right hand (aqua or gray) panel contains the tools.

Note the "Help!" button to your right, near the bottom of the tools panel. Click on this at any time to find out how to do things. "Megahelp" gives you all of the help at once.

You create circuits by clicking and dragging circuit elements from the tools onto the playing surface. Once on the playing surface, you can change their size by clicking and dragging, or by right-clicking.

Drag a wire onto the surface. Click and drag on an end of the wire and watch it lengthen.

Drag a resistor onto the playing surface. Click on "Show values" in the tools panel to see its resistance. Right-click on the resistor, choose "Change resistance" and change its resistance with the slider. You can also type a value in for the resistance, if you find the slider annoying.

The dashed red circles are places where you can join two circuit elements. Try joining a circle on the wire to a circle on the resistor. Note that the circle turns gray when they are joined.

Drag a battery onto the surface (It's really a cell, but who am I to argue with somebody with a PhD in physics). In the tools panel, click on "Voltmeter." Confirm that the voltmeter works by placing the leads from the meter on the circles on the ends of the battery. Note that the default voltage is 9V. How can you change the battery voltage? You guessed it, by right-clicking. Try it.

These are the basic things you need to know about the program. Notice there is also an ammeter. The ammeter must be entered into the circuit. There is also a "non-contact" ammeter which only needs to be moved over a wire.

The Lab: Read through all of these instructions before beginning.

1. Look up Kirchoff's (2) Laws for a circuit in your text or on the web somewhere. There is one for currents and one for voltages. We use these principles to analyze our circuits. Write them down.

2. Write down Ohm's law. It is generally true for our circuits, at least within the range of normal operating temperatures.

3. Using the Circuit Construction Kit, construct a Series (all circuit elements in a single "loop") circuit that contains one 25 ohm, one 50 ohm, and one 100 ohm light bulb or resistor. Add a 100 V battery to your circuit and a switch, and complete the circuit. Remember you can drag the wires to lengthen them. You can right-click on a junction to split it and add a new element, if necessary. Arrange your circuit so that it is easy to see all of the elements.

4. Draw your Series circuit in schematic form. You may use the "Schematic" option to view the schematic of the simulation.

5. Use the voltmeter to record the voltage "dropped" by each circuit element with resistance. Record it neatly on your diagram, or in a table near your diagram. Write the equation for the voltages. Use the ammeter to record the current through each resistor. Write it neatly on the diagram, or in a table near your diagram.

6. Write an equation for the circuit. It should be in this form:

Source Voltage - Element 1 current*Element 1 resistance - Element 2 current*Element 2 resistance - Element 3 current* Element 3 resistance = zero.

You may click on "Show equations" but be aware that it might confuse you because it shows a term in the equation for every item in the circuit, including the wires which have no resistance in this circuit.

7. Create a parallel combination circuit with your 50 ohm, 100 ohm and 25 ohm resistors all in parallel. Maintain the same 100 V battery.

8. Draw a schematic of your circuit and record the Voltage dropped by each resistor as well as the current through each resistor.

9. Find the total resistance of the entire circuit. Show your work.

10. Show mathematically that the voltage dropped by each resistor in the parallel branch is equivalent, even though the current is not.

11. Show mathematically that the sum of the currents through the parallel branch equals the total current.

Bring your paper to class on Wednesday and be prepared to discuss the lab.