Evolution of a Physics Lab

When I think about the physics labs I teach, I realize things have changed over the past 18 years. The way that I run introductory labs is different than when I first started. Here is a review of my lab philosophy over the years.

I’m going to leave off the labs I taught as a graduate student since I wasn’t really in charge of the lab design.

Phase 1: Mostly Traditional – But With Computers

Really, when you first start off with a tenure track position you have to go with the flow. You can’t jump in and start doing crazy stuff. There are too many other things to focus on (grants, papers, projects…). So, for me—I just took the departmental physics lab manual and started with that. It was pretty traditional.

But I quickly set out on my own. I stopped using the lab manual and made my own labs. Oh, they were still pretty traditional in the format of:

  • Here is some physics theory.
  • Here are detailed instructions on how to collect data.
  • Here are detailed instructions on how to analyze the data.

However, my labs had data acquisition stuff to make it cooler. I found some money to put new (at the time new) iMacs in the room and used Vernier Logger Pro with sensors and stuff. Wait, I actually have a picture of this room from 2003.

Check that out. Those are some classic iMacs. Those suckers were in use for at least 10 years.

There was another important aspect of this “phase 1 lab”. I wanted to have the students work on the following:

  • Physics concepts
  • Data analysis
  • Error analysis (uncertainty)
  • Technical writing and communication
  • Experimental design.

Note: you can not do this many things. It’s either a 2 or 3 hour lab. At most you could focus on two of these things.

In terms of writing, I think I was making excellent progress on this front. I was working on an idea about peer evaluation of writing. The basic idea is that students evaluate other students writings as a way of helping everyone write better. I still think this is a good idea, but I moved on (because of many issues and other things to work on).

Phase 2: Make Pre Lab Great Again

If you have taught labs, you know that students aren’t always properly prepared. Most faculty know this. They might spend the first 30 minutes of lab time with a lecture to cover the important points. But this still doesn’t work. It’s hard for the students to pay attention and to fully grok the lab. They end up just asking questions about stuff you just told them.

OK—I can fix this. I will just make super awesome lab materials and post it online. Note only that, I will include videos and everything. Students will look at this and then we can just rock and roll during lab.

Nope. That doesn’t work. It doesn’t matter how great the video teaches the concept if students never watch it. In fact, I would find many students watching the video IN LAB. This drives me crazy—mostly because I hate hearing my own voice.

I tried online pre-lab quizzes. That didn’t work. They would just do the bare minimum to get the stuff done before class. It was just a pain in the rear.

Oh, what about pre-lab quizzes in class? Again, those are more trouble than they are worth.

Phase 3: Play and Compete

This one works fairly well. Forget about the pre lab stuff. Drop the lecture at the beginning of lab too. Give the students stuff to play with and see if they can come up with their own questions.

Here is an example in the realm of 1-D collisions.

  • Show students the tracks, carts, and different bumper options.
  • Tell them “keep the track level”, but otherwise just play with it.
  • Students love the magnetic bumpers. Many of them will try collisions between different mass carts.
  • After they have played, suggest they try to calculate the kinetic energy and the momentum of the carts.
  • Let them come up with their own methods for calculating velocities (I give some options).

That works fairly well. Some students don’t do too much, but for the students that find cool stuff it works great.

Here is another example with a competition. Again, no pre-lab.

  • Show students an inertial balance (oscillates back and forth).
  • Let them play with it.
  • Now for the challenge. Can you use this to find the mass of 4 unknown masses? The quiz at the end of the lab is just finding the mass. Your score is based on your accuracy.

This works fairly well—but not every lab can be in the form of a contest. However, students love to compete and it’s fun.

Phase 4: Free-for-all

This is where I am at now. I don’t expect students to prepare for lab because I will just be disappointed. The labs are a combination of all types of lab. Sometimes they are just verifying an equation. Sometimes they get to build stuff. I don’t expect the lab to match up with the lecture course (because apparently that doesn’t matter).

Sometimes labs still suck, but sometimes they are awesome. I will keep changing my labs until everything is perfect.

Oh, here is a more recent picture of the lab.

Analysis of a borked lab

It happens all the time. It even happens to you. There is a new lab you want to try out—or maybe you are just modifying a previous physics lab. You are trying to make things better. But when the class meets—things fall apart (sometimes literally).

Yes. This is what happened to me this week. And yes—it’s OK.

But let’s look at the lab and go over the problems so that I can make it even better for the future.

Finding the electric field due to a point charge

This is a lab for the algebra-based physics course. It’s always tough because many of the first things they cover in the lecture class don’t have lab activities with things you can measure. Oh sure—there is that electrically charged clear tape lab, but it will be a while before they get to circuits.

So, my idea was to have the students use python to calculate the electric field due to a point charge. This would give them a safe and friendly introduction to python so that we could use it later to get the electric field due to other things (line a dipole or a line charge). It would be great.

Here is the basic structure of the lab (based on this trinket.io stuff that I wrote – https://rhettallain_gmail_com.trinket.io/intro-to-electric-and-magnetic-fields#/introduction/vector-review

You can look at that stuff, but basically I give a workshop style presentation and have the students do the following:

  • Review vectors. Add two vectors on paper (not with python).
  • Find the displacement vector – given the vector for a point, find the vector from that point to another point (the vector r).
  • Find the unit vector and the magnitude of a vector (using python).
  • Next, find the electric field due to a point charge for the simple case with a charge at the origin and the observation point on the x-axis. Do this on paper.
  • Now do the same calculation with python.
  • Find the electric field at some location due to a charge not at the origin (in python).
  • Use python (or whatever) to make a graph of the electric field as a function of distance for a point charge. Graph paper is fine. If they wanted to, they could do the calculations by hand (or use python).
  • Finally, give a quick overview of the sphere() and arrow() object in glowscript.

So, that was the plan.

Lab problems

Here are the problems students had during this lab.

  • Computer problems. Yes—whenever using computers, someone is going to have a problem. In this case, it was partly my fault. There was one computer that was broken and some other ones weren’t updated. Honestly, the best option is for students to bring their own.
  • I can see that there are some students that just sort of “shut down” when they see computer code. They automatically assume it’s too complicated to grok.
  • Students working in big groups. I hate having 4 students use one computer. That’s just lame.
  • Too much lecture. The first time I did this, I spent too much time going over vectors with not enough breaks for students to practice. I partially fixed this for the second section of lab.
  • Some students were just lost on vectors.
  • Yes, the unit vector is a tough concept.
  • I’ve learned this before—but I guess I need to relearn. The visualization (sphere and arrow) are just too much for many students. That’s why I moved it to the end in my second section.

So, that’s it. I am going to rewrite the lab stuff on trinket.io. I am also going to change my material for the dipole stuff that they are doing next week. Hopefully it goes well. Let’s just see.

Thinking about labs

I need to redo all my physics labs.  They are terrible.  I want to make them even MORE about model building.

With that in mind, I saw this:

 

One sentence labs.  Leave the procedure up to the students.  I think I will need some type of turn in sheet for these labs though.  What about informal lab reports?