[Catalist] Physics Phun - back emf and the simplest oscillator

[Leon Harris]

Here is a blast from the past, perhaps reminiscent of Catalist in its 
earlier days when it was more of a discussion forum than an announcement 
list. (Before social media).

I am cleaning out my old projects drawer, and I found this - perhaps the 
worlds simplest oscillator circuit, and a brilliant way to demonstrate 
back emf. You can light a 90 volt (or 300 volt for that matter) ultra 
low current globe from a 9 volt battery.


The circuit consists of an old relay, (some modern ones have inbuilt emf 
suppression) and a neon globe. When it is connected to a 9 volt battery, 
it generates a few hundred volts of back emf, which runs the little neon 
light. Current produced is in the microamp range, so very safe for 
classrooms.


Have a very great year, Catalistians. I have a year of leave so I know I 
will. I will be continuing in my CAC and other professional groups, so 
will be around the traps.


Leon Harris,

Science Teacher At Large,

STAWA Chemistry CAC representative

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