Tag Archives: labs

Why can’t we follow a recipe?

Chances are you know someone who can’t follow a recipe. When they try your favourite recipe, it comes out as a disaster. Why is that? Why is it that someone following step by step instructions can mess it up so badly?

I don’t know the answer for sure, but I suspect it has something to do with lack of familiarity. It seems perhaps ironic that in order to follow a set of step by step instructions you need to know what you are doing already, but I think that is what is required, and here’s why: If you don’t know what you are doing, you won’t know if you made a mistake, whereas if you have an idea what you are doing, you can recognize mistakes and correct them along the way.

The same is true for lab activities. Many of them are cookbook style, with step-by-step instructions. And foolishly we think, well, how can they possibly screw up? And the answer, I’m afraid, is very easily. Step by step instructions instil a false sense of confidence. Students, like cooks who can’t follow a recipe, assume that they have done each step correctly, because they don’t necessarily have the experience to recognize missteps.

The other day in Biology class we were using the popular pop-beads to simulate mitosis and meiosis. They are good in that they give students a tactile, visual representation that they can manipulate and see the process as dynamic, as opposed to series of discrete steps. But it was a disaster. The set comes with very explicit, step-by-step instructions. But either they could not follow the directions, or they were so focussed on the directions they virtually ignored the beads, or they simply skipped the beads altogether and drew the results from memory, rather than observation.

Next time I try this lab, I will do it very differently. I will introduce them to the beads one day, have them plan out exactly how they would represent the steps, and then on lab day have them make a stop-motion animation of the sequence of events in Meiosis. That way they are responsible for planning it out, and will have an idea what it should look like, so they can recognize mistakes when they arise, and then the videos can be critiqued afterwords to see if there are any glaring (or subtle) errors or omissions.

Now I just have to keep this in mind going forward, and plan ahead knowing that cookbook activities (not just labs) have a built-in human flaw.

Alright, GO!

My grade 9’s are doing ecology first this year, and like last year, I kept the number of teacher-led lessons down to a minimum. But this year, instead of everyone working with invasive species, they are allowed to choose their own project (or projects, the number is unimportant) as long as it address the effects of human activity on ecosystems (one or many), water, and soil, and it must include one original hands-on investigation.

Since the investigation part seemed to be the part that was throwing them, the other day I told them that by the end of the 80 minute period they had to submit a description of what, exactly, they intended to do as an investigation, where and when they would perform it, and what specifically, they would be looking for (qualitatively or quantitatively).

I then told them we had a set of microscopes, dishes, jars, pond water, random soil samples from around the school, and a few litres of simulated acid rain. And then I said “alright, GO!”

I was pleasantly surprised by the inquisitive chaos that ensued, and by the end of the class I had detailed descriptions of most of the investigations, as well as at least a dozen experiments actually under way.

It was a frenetic, chaotic, inquisitive class. As a science teacher, I couldn’t have been happier!

Real EdTech, Part Deux

Yesterday I posted about using portable everyday technology to do simple but spectacular things.

But wait, there’s more!

One of my students was with me in the library two days ago when I posted the microscope video on YouTube. Not only did he subscribe to my channel and post a question about what he was seeing in the video, he also told his friends about it. So when we did the activity in class the following day, almost everyone brought smart phones and wanted me to show them how to do microscope videography.

How cool is that?!

Real Educational Technology

I have mentioned before how I became a convert to smart phones – indeed, I have become a full-fledged cyborg with mine – and I still keep finding new ways to use my iPhone for education.

Just today I got so excited with what I was looking at under the microscope I decided I had to share it. So I whipped out my phone, captured a bunch of clips, edited them, and then posted the result to facebook and YouTube, all from the phone. Now THAT is real-world, authentic educational technology.


(PS – go full screen. It’s high res!)

The Sorcerer’s Apprentice, or Never Use a Formula You Don’t Understand

In my grade 10 Science class I recently gave my students an introductory microscope lab, and in my haste I used a “canned” lab from a textbook. Although there are some good activities in this lab, students are presented with a number of equations for determining FOV and magnification, including:

These equations, at face value, are straightforward – in other words they can plug in the numbers and get an answer. But there I something subtly insidious about them – they are just confusing enough that students are unable to apply these formula correctly later. Why? Because they are overly scripted, making the calculations look more complicated than they are, implying that without the formulas, they would not be able to achieve the “correct” answer. They build a reliance on formula, rather than concepts – and formulas without knowing what they mean can lead to trouble – much like poor Mickey’s spell in The Sorcerer’s Apprentice.*

So after an abysmal assessment (which was in part a setup – I could see they were becoming formula dependent), I gave them the following question:

Both images represent the view through the same microscope, with exactly the same settings. How big is the object in the second image?

Their first question? “Which formula do we use?”

My response was a shrug.

I watched as they struggled – one or two figured it out pretty quickly, but others tried dividing the object width (~12mm) by 7 (and some by 8!), some multiplied by 7, some divided by 40 (the circle diameter), but it was clear they were searching for a magic formula. Some, after scowling for a good long time, finally asked “which units do we use? Millimeters or UM’s?” (Aaaagh! That’s not a U! That’s a µ!)

It was challenging to subtly hint at how to simply measure the object without “giving” them the answer, because I didn’t want them to revert to the mindset of me, the teacher, as the sole gatekeeper of knowledge. Eventually they worked it out. Some estimated, some marked off the length of the object on a pencil or sheet of paper and held it to the millimeter scale, and the cleverer ones borrowed a friend’s sheet and held them together in front of a light. (And those that just used someone else’s numbers, well, I had multiple versions of the sheet, so they invariably had to redo it anyway!)

The next question was a bit more involved. I said the view in the image above was through a microscope with 10x ocular and 2x objective. I then asked what the FOV would be using a 20x objective. Despite my earlier warning stay clear of equations for this exercise, I saw many pulling out the equations from the previous lab. And that’s where they really got into trouble…

Numbers were thrown willy-nilly into the equations in the hope that somehow they were correct. Several students, despite correctly identifying the magnifications as 20x and 200x, wrote out

40 / 200 = 7mm / x

When I asked where the 40 came from, they said “low power on a microscope is 40x”.

“All microscopes?” I asked. That threw them.

Eventually I helped them work out that the higher magnification was ten times the lower magnification, so the view would be zoomed in ten times as close. The FOV should then be 10x as small (which is in itself a tricky concept, students are tempted to say 10 times the magnification means bigger, so the FOV is 10 times bigger). For most it eventually clicked that 10x the magnification means the field diameter is 10x smaller. Simple and no formulas to memorize.

It was remarkable, in a way, that a simple set of four of these questions took them a full 80 minute period – but that was mainly because I wouldn’t let them get away with wrong answers. One could call it a waste of a period, but I would not. It was absolutely necessary.

This is exactly the kind of thing Eric Mazur talks about. I will definitely be doing more of these exercises in the future!

*I mean the Fantasia version. Though that scene is included in the recent Nicholas Cage film.

Indications of chemical change

Some of my students were away when I demo’d chemical changes and how to identify them, so I took a few minutes to record the demos so I could post them.

This is the result:


Microscope Diagram

Many years ago, as a (fairly) new teacher, I made a diagram of a typical microscope that I was rather proud of. The years went by, and my photocopied versions would run low, so I would copy the copies, but the original seemed to have vanished. Well, today while looking for something else, I came across the original. So to celebrate, I am sharing my humble little microscope diagram with the world at large. Enjoy!

Click to download a PDF

Squishy circuits

I have not tried it yet, but with my intro to electricity in grade 9 this coming year I am SO doing this:

Funny thing is, she says “high school physics teachers have been doing this for years” – where the hell have I been?

Here’s the website with recipes for making the different doughs:


Millikan Oil Drop Simulation

Some years ago I wrote a little simulation program for a virtual Millikan Oil Drop lab. Since I have this Blog, I thought I would take the opportunity to share it, in hopes that others will find it useful as well.

It is a standalone Windows .exe file, with supporting documents in PDF. It allows students to practice using the apparatus using either droplets (random mass) or beads (fixed mass), and either the real value of e (1.6×10^-19 C) or an unknown value that is close to, but not quite, the real value.

There are a few nifty built-in features, like speeding up time and a stopwatch that follows the simulation time, plus the ability to adjust the plate spacing and reverse the polarity.

It’s not perfect, and the built-in help file doesn’t seem to display properly in Win7 (the Help.PDF file is the same as the online help), but it does the job adequately. The zip package includes a list of the unknown e values. I would suggest that if you distribute this package to your students that you remove the unknown e values.txt file, though that is up to you as a teacher.

The package can be downloaded here. It is distributed as-is, with no warranty.

If it is useful to you, enjoy!