AP Physics 1 – Virtual Circuits

During this activity you will build simulated electrical circuits using the web based program Circuit Construction Kit: DC – Virtual Lab from PhET.  The goal 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.milliganphysics.com and click on Physics 1 and then Links and then DC Circuit Construction Virtual Lab (HTML5 version).

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.  The circuit should look something like this:

Now use the voltmeter and an 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 the ammeter a part of the circuit.  This shows measuring the voltage of the battery and the current in the wire on the right:

Complete the table below by measuring the voltage across the bulb and voltage from one end of a wire to the other end of the same wire.  Connect another ammeter to measure the current in the other wire on the other side of the circuit.  Record the values here:

	Battery	Bulb	Wire
Voltage:
Current:

Use Ohm’s Law to calculate the resistance of the bulb.  Show work and answer here:

R =


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

Try experimenting with the values of the battery’s voltage.  To change the voltage, click on the battery and use the slider at the bottom of the screen.  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 icon lower right (looks like:  –| |–).  This is how circuits are often depicted – with standard symbols for wires, batteries, resistance, etc.  Also try using the Conventional option for showing the current – the red arrows show the conventional positive current employed by physicists, scientists and engineers around the world.

Feel free to experiment with the controls for Wire Resistivity and Battery Resistance.  However return both of these control sliders all the way to the left (on “tiny” and 0) for all of the following exercises.  By doing this, it is assumed that the resistance of the wires and that of the battery are much much less than that of the other components in the circuit – this is a very good assumption for most circuits.  We will ignore these negligible factors in Physics 1.

Note:  you can reset everything to the defaults and start over by clicking the circular orange button at bottom right.

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 voltmeter and ammeters to measure the voltages across each device and the current passing through each device.  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 a resistance value using Ohm’s Law.  Show work here:

R =

Based on this, it is as if the battery is connected to a single resistor of what value? __________

(This is called the equivalent resistance of the series combination.)

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?  i.e. What do all series circuits have in common?  List your thoughts and observations here:
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 device and the current passing through each device.  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 a value of resistance using Ohm’s Law:

R =

Based on this, it is as if the battery is connected to a single resistor of what value?  ___________

(This is called the equivalent resistance of the parallel combination.)

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?  i.e. What do all parallel circuits have in common?  List your thoughts and observations here: