Teaching young wannabe techs.....

I'ma devoting some skull time to thinking a few teacher thoughts.  Things like..... getting students to really grasp what a Voltage Drop test is, how it works, and when to use it.

What?!?   I can use my Voltmeter to find resistance in a live circuit?   That thar is cRAZY talk!!

Look youngen..... Ohm's law is a friggen LAW.    Voltage, current, and resistance are in lock step.  Change one, and the others will show it.  A Voltmeter only measures the difference in voltage between the leads..... no matter where your grubby paws put them.

If you put those leads on two ends on the same wire that has current flowing through it at 12 volts.... is there any reason to expect one end of the wire to have 12 volts and the other end of that same damn wire to have anything else but 12 volts??

No..... unless.....

What does it mean if one end has 12 volts and the other has 11.8 volts?   Your meter shows the DIFFERENCE between the leads.... what will it read?  .2 volts, or 200 millivolts..... Right?

If there is a DIFFERENCE from one end of the wire to the other..... then that means......??????

RIGHT!   Something got in the way!  We call that 'Resistance' boys and girls.... Resistance.   

So yes, a Voltmeter correctly applied in parallel to a live circuit will show resistance as a difference in voltage between the leads.  The higher the resistance, the higher the voltage difference (Voltage reading).

There.  Let your head stew on that a while.