Virtual Circuits

During this activity you will build simulated electrical circuits using the Java-based  program Circuit Construction Kit from PhET.  The goals of this activity is to get hands on experience with Ohm’s Law, meters, and types of electrical connections.

To get started, go to:  www.farraguttn.com/science/milligan and click on Physics and then Links and then DC Circuit Construction Kit.  It may take a minute or so for the program to start up.

Part A – a Simple Circuit

Start by building a simple circuit that consists of a battery connected to a light bulb.  Simply click and drag the components onto the screen and connect the ends as needed.  If you make a mistake you can click on it and delete it (or even click on a connection and break it by pressing delete).  The circuit should look something like this:

Now use the voltmeter and the ammeter to measure the potential and current in the circuit.  To use the voltmeter simply connect to either side of the item across which you wish to measure.  To use the ammeter you must disconnect a wire and make it a part of the circuit.  Here is what it should look like to measure the voltage of the battery and the current in the bottom wire:

Measure the voltage across the bulb and from one end of a wire to another.  Connect another ammeter to measure the current in the other wire.  Record the values here:

	Battery	Bulb	Wire
Voltage:
Current:

Use Ohm’s Law to calculate the resistance of the bulb:

            R =


Now click on the box that says Show Values and compare your calculated resistance of the bulb.

Try experimenting with the values of the battery’s voltage.  To change the voltage, right click on the battery and choose Change Voltage.  Try increasing and decreasing the number of volts and observe the change in the current.  Also try experimenting with the resistance of the bulb.  You can change its value the same way.  Describe below the effect of voltage and resistance on current:

When voltage is increased, the current ______________________________________________.

When resistance is increased, the current ____________________________________________.

Now try clicking on Schematic and under the Advanced options choose hide electrons.  This is how circuits are often depicted – with standard symbols for wires, batteries, resistance, etc.

Part B – a Series Circuit

Clear the original circuit and start over.  Using the schematic diagram below as a guide, construct a circuit that consists of a battery and two resistors all in a single loop.  In this case we say that the resistors are connected in series because current passes through them one after the other.  You will need to change the voltage of the battery and the resistance of each resistor to reflect those shown below.

Use the voltmeters and ammeters to measure the voltages across each resistor and the current passing through each resistor.  Record the results:

	Battery	R1	R2
Voltage:
Current:

Try applying Ohm’s Law to each resistor separately.  Does V = IR in each case?  Use the voltage and the current of the battery to calculate resistance using Ohm’s Law:

            R =

It is as if the battery is connected to a single resistor of what value?  _____________________

Try experimenting with three or more resistors connected in series and/or with multiple batteries in series to look for common properties of series connections.  Measure the voltages and currents as before.

What generalizations can be made?

Part C – a Parallel Circuit

Clear the series circuit and start over.  Using the schematic diagram below as a guide, construct a circuit that consists of a battery and the same two resistors, this time connected in parallel.  In this case there are junctions where current can “split up” or run “together”.  You may need to change the voltage of the battery and the resistance of each resistor to reflect those shown below.

Use the voltmeters and ammeters to measure the voltages across each resistor and the current passing through each resistor.  Record the results:

	Battery	R1	R2
Voltage:
Current:

Try applying Ohm’s Law to each resistor separately.  Does V = IR in each case?  Use the voltage and the current of the battery to calculate resistance using Ohm’s Law:

            R =

It is as if the battery is connected to a single resistor of what value?  _____________________

Try experimenting with three or more resistors connected in parallel and/or with multiple batteries in parallel to look for common properties of series connections.  Measure the voltages and currents as before.

What generalizations can be made?