6 Lab 1: DC Circuits

Acknowledgment

This project is made possible with funding by the Government of Ontario and through eCampusOntario’s support of the Virtual Learning Strategy. To learn more about the Virtual Learning Strategy visit: https://vls.ecampusontario.ca.

PHY137 Stay-At-home Experiment 1

DC Circuits

What you will do

Build simple circuits using batteries, light bulbs, and wires. Explore the relative resistance of the light bulbs, and then compare it to the resistance of the wires.

What you will need

• 2 AA batteries with battery pack
• Alligator wires
• Incandescent light bulbs with sockets
• An unchanging reference of brightness: a piece of white paper with unchanging illumination (for example, illuminated uniformly by a desk lamp), or an indicator light that has an unchanging brightness (such as the power indicator of a power strip)
• Tape

Demonstration Video: https://youtu.be/Enw6-jIGATk

Procedures:

Part I – Light Bulbs in Series and in Parallel

1. Install the incandescent light bulbs firmly into the light bulb sockets. Be careful not to tighten the light bulb too much (you might break it).
2. [VERY IMPORTANT] When you connect alligator wires to the light bulb sockets, you need to make sure that the clamp does NOT get into contact with the barrel of the socket. Examine the structure of the socket, and briefly explain why you should avoid the contact.
3. Draw the circuit diagram of two light bulbs in series powered by a battery.
4. Put two batteries into the battery pack. Use the alligator wires to form a circuit in which the batteries power two light bulbs in series.
5. Place the circuit beside the unchanging reference of brightness, take a photo of all lights including the circuit. Try to let the camera optimize exposure using the unchanging reference (on most phone camera apps, you can do this by tapping on the reference.)
6. Draw the circuit diagram of two light bulbs in parallel powered by a battery.
7. Use the alligator wires to form a circuit in which the batteries power two light bulbs in parallel.
8. Place the circuit beside the unchanging reference of brightness, take a photo of all lights including the circuit, while letting the camera optimize exposure using the unchanging reference.
9. Attach the photos in your lab report, and explain why the pair of light bulbs are brighter in one of the photos (Step 3 vs. Step 6).
10. For each photo, briefly explain how you can tell the difference in resistance between the two light bulbs. If you do see a difference, identify the light bulb with the higher resistance. (Note that Incandescent light bulbs have different resistance at different brightness levels. Your answers for the two photos might not be consistent with each other.)

Part II – Compare the resistance of alligator wires and those of the light bulbs

1. Use 2 batteries to power 2 incandescent light bulbs in series using three alligator wires. Take a photo of the light bulbs beside the unchanging reference of brightness. Put this photo in your report.
2. Remove one of the two light bulbs by disconnecting the alligator wires
3. Add one alligator wire into the circuit in series with the remaining light bulb. Take a photo of the remaining light bulb and the unchanging reference.
4. Repeat Step 13 until you have all alligator wires in series in your circuit.
5. For all your photos from Step 14, crop the photos to keep only the light bulb and the unchanging reference. Put all cropped images side-by-side in your report.
6. Can you estimate the approximate ratio between the resistance of the removed light bulb (at its brightness level in Step 11) and the resistance of one alligator wire? (To put it another way: how many wires will have a similar resistance as the removed light bulb?) Briefly explain.
7. Can you estimate the approximate ratio between the resistance of the remaining light bulb (at its brightness level in Step 11) and the resistance of one alligator wire? Do more tests and take more photos if necessary.
8. (Bonus +1 mark, not necessary) You can open your photos with ImageJ and move the mouse over various pixels to read the RGB (red-green-blue) values of the pixel. The average of the three numbers in the RGB values gives you a numerical estimate of the brightness of the pixel. You can now read the numerical brightnesses of the light bulbs in Step 11. In addition, you can plot the brightness of the remaining light bulb against the number of added wires. With the curve, you can make more precise estimations of the resistance of the light bulbs.

Tips for data analysis:

• Attach all photos that are required in the procedures above. Do more tests and add more photos if you think they can help you explain better.
• Answer all questions in the procedures above.
• Attach graphs or tables when necessary.
• Make a reasonable conclusion based on your results.

Suggested topics for discussion:

• Can we compare other resistances (qualitatively) using the same experimental components?
• Can we do some simple quantitative calculations using the same experimental components?
• Can we do some quantitative calculations with some additional components at low cost while staying at home?

We value your feedback!

Did you enjoy this experiment? What are the aspects that you dislike the most about this experiment? – Let me know in the “Student Feedback Survey for Lab 1” on the discussion board on Quercus! We may award the most helpful inputs with +1 bonus mark for the lab report!

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