Feb 26, 2009

Digital instruments - more accurate?

Putting the physics/chemistry teacher hat on again. Today, my SL chemistry class tried to determine a value for the specific heat capacity of water using Vernier probes, graphing software and (hopefully) their brains. It was the first time I got the new GO sensors out of the box so in doing my prep, I happened to have two sensors connected at the same time. I took a picture of what the software told me.


So what we have are two probes, in the same room telling two temperatures that are (by my standards) not even close to one another. I showed this to the students whose dumbfounded reaction implied I was performing some kind of science voodoo magic.

Quite often, when the 19th century skill of thermometer reading is required in a lab procedure, students will identify the thermometer as a weakness and suggest using a digital thermometer is more accurate. They are wrong on two accounts as I tried to explain today.

First, the students are confusing the meaning of accuracy and precision. I will concede that these digital probes may in fact be more precise (one needs to be careful here). Secondly, as the above result indicates, these probes are hardly accurate (or at least they can't both be). My question was "which reading is more accurate?". Of course, you can't tell (and in fact, a conventional alcohol thermometer read about 22 degrees - adding more fuel to the fire).

The point here is, students trust technology more than they should. They believe a digital probe is more accurate than a conventional instrument in most cases - this dogma evidenced by the massive confusion over why two digital instruments might disagree (one must be broken said one student).

We need to be careful about what we are really teaching them?

2 comments:

Kim Cofino said...

OK, so here's my devil's advocate point of view (please excuse any basic science ignorance - it's definitely not my field of expertise). Wouldn't you need to use two conventional thermometers in the same two locations in the room as the digital probes to really do an accurate comparison? Could one of the digital probes been near a breezy spot in the room, or the other near a more stifling spot? Just a thought!

David Young said...

@ mscofino: careful how you use the word "accurate" It should be a "scientifically valid" comparison and yes, I could collect more data (better to stick a bunch of probes in a beaker of water). The point was that they can't both be accurate but kids believe them to be MORE accurate than old style thermometers.

Both probes were side by each, less than a cm apart, on a desk. (no AC, it is winter here)

Post a Comment