Physics Core/AP 1 and 2

Physics Lab

# Physics Lab: Simple Circuits

## Goal: To construct and compare a simple parallel and a simple series circuit

#### Materials

• Insulated copper wire
• 2 small light bulbs (1.5 V) [like flashlight bulbs]
• 3 AA (1.5V) batteries or a 9V battery
• Cardboard or sockets for your bulbs
• Rubber bands (if you don't have sockets)
• Aligator clips or metal paper clips
• A multimeter (capable of measuring voltage and current)

#### Procedures

Construct both circuits:

• A series circuit with two lights in series, connected to a battery.
• A parallel circuit with two lights in parallel, connected to a battery.

For each circuit:

1. Plan the circuit and draw the circuit diagram.
2. Construct the circuit following your diagram; if you need to change the circuit to make it work, update your circuit drawing and explain why your original plan did not work.
• Use the cardboard to hold the light bulbs at a specific distance if you do not have bulbs with sockets.
• Bend the paper clips around the base of each bulb to hold it in place, or use the aligator clips.
• Cut the copper wire to convention lengths to connect the components of your circuit.
• Shave some insulation off the wire ends so that you can make good contacts with your circuit components.
• Use the rubber bands to hold the wires to your bulbs or connect the wires to the bulb sockets.
• Bend the other ends of the wires so they will hook around the battery terminals or use rubber bands or tape to fix the wires to the terminals.

Caution: Do not leave your system connected for more than a few minutes at a time or your circuit will overheat.

• Demonstrate that the circuit works (i.e., the light bulbs light!)
3. Use the multimeter to determine
• the current flowing through each device on the circuit
• the potential difference (voltage) over the battery and light.
4. On your circuit diagram
• identify the current flowing through each device
• potential difference before and after each device.
• Unscrew one of the light bulbs. What happens?
5. (Optional) Construct lemon battery from the HILA Science Camp projects site.If you have the materials, see whether you can light multiple bulbs. How does the lemon circuit compare to the battery-powered circuit?

6. (More optional activities): If you are really excited by the possibilities of experimenting with electrical power, you will need an electrical board which allows you to quickly assemble components. You can buy a commercial one. The best of these are the Radio Shack umpty-five-experiments-in-one-box electrical kits, which often include builtin voltmeters, battery racks, buzzers, speakers, lights, switches, and LEDs. However, you can rig something similar by following the instructions for the basic electroboard at the SchoolNet support site.

#### Data Handling

1. Calculate potential based on current measurments and your circuit design. How do your calculations compare with your voltage source?
2. Create accurate diagrams of your circuits using conventional circuit symbols (see text for examples).
3. If you were able to use an ammeter, calculate the current on each wire in at least two circuit layouts, and compare the calculated with measured values. Explain any differences.

#### Report

1. Describe your materials, equipment, and procedures in sufficient detail that your fellow students could repeat your experiment.
2. Report your data. This should include your circuit diagrams, your predictions of circuit behavior, and the actual circuit behavior. Be sure to indicate the amount of error in your measurements. For example, if you can only measure a current of 25amps within 1 amp, your error would be 25 ± 1, or 1/25 = 4%. Present your data in an organized form, preferably in a table, in such a way it is easy to compare results as you repeate trials or vary a specific contributing factor.
3. Show a sample calculation, if you have calculated values.
4. If you did a series of experiments, varying something by increasing or decreasing a factor, try to plot your data (y-axis) as a function of the factor (x-axis).
5. You may use a spreadsheet to calculate your information and create your table.
6. Summarize your results.
7. Draw conclusions about what is happening.
8. Suggest at least one way to improve your experiment.