I realize this is probably a very simple question, but for some reason I'm getting very confused.(adsbygoogle = window.adsbygoogle || []).push({});

1. The problem statement, all variables and given/known data

A motor is connected to a 12 V dc supply and draws 5.0 A when it first starts. What will be the back emf when the motor is operating at full speed and drawing 1.2 A?

2. Relevant equations

R=V/I

Source voltage= IR + Back EMF

3. The attempt at a solution

I realize you just have to use Ohm's law and solve for resistance, and then plug in that resistance and current and source voltage into the second equation and solve for Back EMF. What I'm confused about is which current I plug in where. I think I would plug in the initial current (5.0 A) to solve for resistance and then use the second curren (1.2 A) in the second formula to find back EMF, but I'm not completely sure as to why, so I would really appreciate an explanation.

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# Homework Help: Circuit/Back EMF question

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