Chromatography, Cellulose, and Water Potential
Welcome to the second issue from Wyndia’s Wonder Workshop. Today we wonder on (i) how to make up for some of the lab-loss we had last year by using one of my innovations, and (ii) the best learning strategies we can follow.
Recall from my first blog in this series on Wyndia’s Wonder Workshop, the at-home mask tester uses chromatography, much like pregnancy sticks. To make it work, I had to end up using locating agents too (Harwood & Lodge, 2014). From this project I understood chromatography at a different depth. When we design any product, we will come across all kind of problems. The textbook makes it look simple, but the glue I used on the test stick reacted and contaminated my results, and I had to get a different glue. And later in Biology class, I learnt that my innovation increases the water potential (Jones & Jones, 2014) besides increasing reaction rates. And we can see a trend here: Project-based learning helps us connect the dots not just within the subject but many times across subjects too. And the industrial tester allowed me to make connections between mechanical engineering and biology: My design to mimic the human lungs made me realize the power of the intercostal muscles and the diaphragm muscles and how engineering needs to cope with much less. To explore the wonders of chemistry please see the blog by our educator Mr. Mahesh Kumar (Kumar, 2021).
With such project-based learning (PBL) there is a downside. It takes way too long when compared to text-based and classroom-based education. There is an intermediate mode of learning that is hands on, and it takes lesser time than project based learning but more time than classroom learning: lab based learning.
Unfortunately, Covid-19 has eliminated this lab mode for us for the last year. So, to cope with that loss, I have created this project titled Countering Covid-Loss with at Home Innovations.
Countering Covid-loss with at Home Innovations – Part 1.
Today we are creating a vernier caliper with everyday materials, and we are making up for some of the lab-loss this year. I am going to present the details of a simple device that can be done in 30 to 45 minutes once the needed materials are assembled. And the best part is this: we need just three steps to assemble this device.
The basic idea behind vernier calipers is simple. You have a second scale that is a scaled version of the main scale (Sang, 2014) and the scaling factor is typically 0.9 i.e., each marking on the second/vernier scale measures 0.9mm while each marking on the main scale measures 1mm. You can download a scaled version from here. The vernier calipers improves accuracy by measuring the portion that lies between the two adjacent millimeter markings on the main scale. This part is obtained by first locating the markings that line-up well between the two scales, and then counting the number of markings we needed to traverse.
You have a choice here: (a) Import a ruler into a document and print out the ruler with scalings of 0.9 and 1.0, or (b) print out the file you can find here. You would also need some cardboard, glue, cellophane tape, scissors and/or paper cutter knife. I started with these materials.
Step 0. Assemble the materials Needed.
Check your print out for the main scale against a standard ruler. If they don’t align because of enlargement/shrinkage on the printer, please do not be discouraged. Just continue with the steps below. Let’s term these small units on the main scale that don’t align with standard scales as wm (WyndiaMeters). We can obtain a scaling factor as illustrated in Appendix A. And then use that scaling factor to convert wm to mm.
Step 1: Build the main scale and assemble the jaw on the main scale.
Build the main scale with the print-out that is not scaled by a factor of 0.9. Alternately, use a regular ruler but that would necessitate further tweaking of the slider mechanism presented here. Next add a vertical cardboard at the beginning portion of the ruler to mimic the left jaw. We don’t have to aim to make it exactly 90°. We will fix the error arising from this imperfection in perpendicularity. This is a rapid version: we need to be careful only about the width of the two rulers being even so that the slider mechanism works well. Rest of the alignment issues can be built into zero error.
Step 2: Slider mechanism – part 1:
Flip the main ruler and place two stripes of cardboard (the blue ones marked ‘1’ and ‘2’) on both sides of the main scale snugly. These two stripes are part of the slider mechanism. Connect these two stripes using two other cardboard pieces like the pink ones (marked ‘3’ and ‘4’) in this figure.
Step 3: Complete the Calipers
Here there are three sub-steps. (a) Now flip over and add another stripe of cardboard to secure the slider to the main ruler (the long pink strip in the figure). (b) Then affix a thin cardboard stripe to the jaws and cut it: this contact mechanism removes errors from non-perpendicularity of the jaws and sends that error to the zero error (the small pink tabs seen on the jaws). (c) And then cut a 0.9cm to 1.8cm (10 to 20 fine markings) portion of the vernier scale we printed out earlier and affix it to the slider carboard as shown in this figure. Also notice that the zero error for this scale is 1.9mm. Notice that we don’t need to align the vernier scale exactly on the horizontal axis. These nonalignment errors too work their way into the zero error. As to the angular alignment: notice that there is a slight angle between the two scales. Such small misalignment is ok. By using trigonometry, I worked out the errors and it is much less than the accuracy of these calipers. Say there is 1° error in alignment it only affects the accuracy by a maximum of 1.5μm and that does not impact this caliper’s accuracy of 0.1mm.
Step 4: Using the vernier calipers
This is the simplest part and the figure is self-explanatory for those of us who did Physics.
Diameter of the cap is 22.8mm – 1.9mm = 20.9mm. (test yourself: why did I subtract 1.9mm?).
Step 5: Going Beyond the Basics
We can take it further buy using additional kirigami-like techniques, and additional materials: I used tin from toothpaste tube to make the jaws realistic. And this version of the calipers can be used to measure inside diameters too.
The Big Balance
Clearly, we don’t have to reinvent the wheel: classroom and textbook learning helps us learn quickly and even cram. The learning to effort (L/E) ratio is very high for classroom learning in the short term. PBL does do quite a bit of re-inventing the wheel but in the process, we end up innovating some non-wheels too.
At the next level, with a lower L/E ratio is lab-learning. Imagine seeing the bright yellow precipitate in a chemistry lab that we missed this year! Or imagine the bright memories when our teacher would have intervened to throw things in the flame-hood if we had messed up rather accidentally. Lab-learning, where educators have put in the effort to make hands-on learning easy, takes more time than classroom and textbook learning. A 45-minute measurement lab that we missed would have had our hands acting on both vernier calipers and micrometer screw gauge.
And we have project-based learning that takes even more time. We have spent 45 minutes just on vernier calipers alone today but in the process learnt a whole lot more about errors than what is discussed in the text. How do you feel about the value you got given the time you had to spend on it? Did you experience any additional difficulties?
This activity is much more time-consuming than the in-classroom learning we did on vernier calipers a few months ago. And when compared to the lab-based learning that we missed out on, typical PBL is even more time-consuming. But retention is highest for PBL because to make the project work, we needed to immerse ourselves in both the theory and the practice, and fix the shortcomings. It is like combining both classroom-learning and lab-learning with an array of fixes. We need to fix problems that we don’t see addressed in textbooks. Here, we fixed the errors from jaws not being perpendicular besides putting together the slider mechanism. We also analyzed the errors from slight rotational misalignment between the two scales.
I am wondering what the correct mix is for using these different types of learning. What is the balance between these modes of leaning? Please weigh in with your thoughts on how best to we can learn. Please reach out to me by email. I will reply during the holidays.
When printing out the scales we may experience another difficulty: the printed main scale may not align with a standard ruler. We can work around that. First let’s term the smallest markings on this regular scale that does not align with any standard scale as wm (where wm stands for WyndiaMeters). Just measure and operate in wm and then finally use a scaling factor to convert to mm. Measure say 200 units of wm on a standard scale and let’s say that measures 202mm. Then by applying a conversion factor 1.01 we can convert from wm to mm.
Chromatography: separation of solutes in a solution by putting them through a medium in which the flow rates differ and they settle at different locations in that medium. Many times a locating agent is needed to visually locate the separated solutes.
Kirigami: Origami plus paper cutting.
L/E ratio: Learning to effort ratio.
Locating agent: A locating agent is any chemical that is used to detect another colorless chemical. The locating agent reacts with the colorless chemical and produces products that are colored.
PBL: Project based learning.
Water potential: Water moves from places where water potential is higher to places where water potential is lower. The potential difference arises because of solute gradients.
WyndiaMeter: abbreviated as wm. Denotes any regular linear measurement units that do not align with any standard scale such as mm-ruler or inch-ruler. These units enable us to work with non-standard even markings arising from poor printing.
Harwood, R., & Lodge, I. (2014). Cambridge IGCSE chemistry coursebook (pp. 32,33). Cambridge: Cambridge Univ. Press.
Jones, M., & Jones, G (2014). Cambridge IGCSE biology (3rd ed., p. 31). Cambridge: Cambridge University Press.
Kumar, M., 2021. Chemistry Without Walls. [Blog] Legacy School Blogs, Available at: <https://lsb.edu.in/chemistry-without-walls/> [Accessed 21 May 2021].
Sang, D. (2014). Cambridge IGCSE Physics (2nd ed., p. 5). Cambridge: Cambridge University Press.
About the Author:
Wyndia is a Cambridge learner who has a very strong passion for science and snowboarding. Many people like fall for the beautiful colors and summer for the pleasant weather but I like winter for its snowy slopes. In fact, my love for science probably came from skiing down these slopes every winter. In physics you learn how acceleration and gravity affects snow sports, for chemistry you learn about the hexagonal shapes of snow and for biology you learn about how the flora and fauna have adapted to these cold conditions. Some people get inspired by celebrities and famous historical figures but I believe nature is our biggest inspiration.