spike

I setup two small circuits on breadboard with BD139 transistors to drive a 12v 0.2A motor and 24v 0.15A Relay to learn transistors, I can switch ON transistor through base resistor using 3.3v PSU. I know when motor/relay stops it can push back some current and i believe its called current...

I am tasked with confirming a report that said we had a large voltage spike (~400v I believe) when turning some equipment on. I went and put the oscilloscope on our main that is in the same box for the switch for the equipment. I throw the switch and see my measurements react a little but I...