Your switch is in parallel

I do not know how many times I have had to tell students over the years that their switches are wired in parallel, not series. They will come up to me and say “My lights are on and work when the switch is turned off, but when I turn it on everything turns off.” This spurs me to inquire what they mean about everything, and then telling them they have the switch wired wrong and that they need to start over. They never believe me the first time, but they are ready to learn.

As a physics teacher, I have noticed that when we get to sections on wiring, students will be able to read a wiring diagram and use Ohm’s Law and Kirchhoff’s Rules to solve problems, but they lack a physical understanding of how the very basic circuits work. The problem with the standard model of teaching is they see things in lecture, and then do a few things in a very controlled lab exercise where one person might be able to hook everything up for the other students in the group. The other issue is that much of the equipment turns into a magic black box that just works, giving the students a belief in magic instead of the ability to create something as simple as a switch on their own. To help counteract this, I find it important to require all the students to complete what we call a wiring project.

This is something that I was exposed to as an undergrad at Radford University. The professor, Dr. Rhett Herman, would set up old rusted metal shelves, put some D batteries on top, give us some wire, and tell us to create something. After the inevitable “create what” wears off, students would get down to figuring out how to actually wire things. Since thing things have evolved and we now have new shelves, and provide power lines with 7V AC. We also give them cardboard, hot glue, LED’s, motors, diodes, bread boards, mini-light bulbs, copious amounts of wire, and answers to their questions.

The basic requirements are that they come up with some theme for the project and that it incorporates both series and parallel circuits, LED’s, a motor, and a switch for each group member. For some students this is the first time in a year long course that they get to express their artistic side, while for others they want to show they can engineer something amazing from cardboard and tape. It is a lot of fun to see the students who have been working math problems for me all year to start showing creativity outside of problem solving.

When the project first starts we get many blank stares, and students who think they can put it off because “how hard could it be to turn a light on.” So they are goaded to work and inevitably one group will take the plunge and start building, taking wires in hand while risking what they think will be a fatal electric shock, and start connecting things, hoping for the best.

After a few weeks there will be a mad rush of all the students using all their free time (yes, this is completely outside class time project, and they all work on it and enjoy it) to make something amazing.

It is interesting to watch the project develop because many of the students can solve equations and draw diagrams, but when it comes down to asking them to hook up 3 LED’s in series, or 3 light bulbs in parallel, they will struggle. The problem I see the most is with switches. Since switches are sealed (most of them) students do not see that it’s a physical metal toung connected to an insulator that rotates back and forth to make contact with another piece of metal inside the switch. They see that they have 2 wires, the switch has 2 terminals, and decide to hook a wire to each terminal. They learn quick, and the best part is that often I help one group and then see that knowledge passed on to the different groups. I think that is one of the most rewarding things to see, students taking time out of their day to help another student in need!

Overall the project helps get students gain an understanding of basic circuits. No programming needed, artistic ability of all accepted, and in the end we show off all the projects to the students to many smiles and laughs. All in all a good time for everyone!

 

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Students created a scene from Disney’s Frozen. You can see Olaf and Elsa are attached to motors so they can spin, while the background has LED’s in it to make a star filled night background.

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After having some difficulty building an amusement park, this group decided to blame the tornado located below their project for the damage, and claim to have moved to a new location as part of their theme. The ticket booth, ferris wheel, and dunk tank light up, the carousel rotates, and there is a ring of fire to jump through in the background. A unique way to tie multiple projects together.

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Every great movie should have a wiring project tribute to it. This group had a light-up sign, barn lights, and a tornado that realistically shook the entire shelving unit! This project was located below the wrecked amusement park.

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A few shelves over, you can see the new amusement park in all its glory (build by a different group) and complete with rotating ferris wheel, light up concession stands, and carnival games.

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This group took a popsicle stick, attached it to a regular switch and the tied a rubber band to it. When you pull the arm on the slot machine the reel starts to spin, and stops when you let go. A neat job of engineering their own slot machine!

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This group had a water wheel that had to be spinning before any of the other lights came on! A nice job of promoting alternative energy!

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Here you can see a dog chasing a squirrel around the tree, with a nice tree house, stars in the sky, and if you look close on the left you can see they used yellow LED’s to act as the lights on lightning bugs!

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This group wanted to answer the question of why aliens always abduct cows. They managed to take two pie plates, some styrofoam bowls, and some wire to make their UFO spin and still light up. It is amazing what you can do with random stuff from around the house.

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Everyone loves the Pokemon Center Base. This group actually made an escalator that worked completely out of cardboard.