Turning on diodes in class. Teacher's Note Pro Preview

TL. DR.

Turn on one diode at a time to avoid burning them all because of the same mistake. If it is not working switch cable ends.

Turn on one diode at a time

If all the students make the same mistake and they burn out the diodes that you would have to replace them. To avoid this you can group the students around a single set and turn the first diode together and then allow the students to copy their solutions

Don't show the solution yourself

A big mistake is to gather the students around you on a table and to show them how it's done. Rather than doing this, you can gather them around one of the teams in the group and watch them and direct them and instruct them how to do it. If one of the diodes burn out you would have to replace only one, not all of the diodes. 

If the diode does not turn, try switching the cable ends

The diode has a shorter pin and longer pin. These are the "Plus" and "Minus" of the diode. The Cathode and Anode of the diode. We've not discussed with the students what is a Cathode and what is Anode. This is something we will do in other sections, but not now. If you feel prepared you could always try to explain it to them, but be prepared that you could lose them if you enter into too many details. And it is also the principles that matter, not the names. 

Burn out a single diode

It is worth the experiment and time to burn one of the diodes and to show this to the students. It will cost you a couple of cents, this is true, but is worth it. We would describe in another teacher's note how to do it and again why.