# Relating DC motor with the Fleming right hand rule

I am studying DC motors and I know that what the direction of the rotation will be given by the left hand rule.

If I compare the right and left hand rule, if I point the thumb and the first finger to the same directions with both hands, only my second fingers will be in opposite directions (the current).

So I am wondering if I suddenly cut the current of the motor, then it will still be in motion due to inertia, then the right hand rule apply and a current will be induced in the opposite direction of the current that I was supplying. Does this mean that I need to protect my circuit against reverse current? Or am I getting everything wrong?

Why this adafruit circuit doesn't protect against reverse current? It does the opposite, it protects against inducted current in the same direction:

Yes, indeed.

That's why flyback diodes are used to protect the transistors used for switching current off or on to electric motors.

• Actually diodes are used if the current stays in the same direction. I am reading more and I think the motor works as an inductor, and all the drawings of the left and right hand rules are wrong, because in the place of the current is actually voltage, so the voltage is the one that inverses (as the motor will work as a generator), not the current (at least I think, I am not sure). If you see this circuit: learn.adafruit.com/adafruit-arduino-lesson-13-dc-motors/… the diode only makes sense if the motor keeps the current in the same direction when the transistor is off Feb 23, 2017 at 21:04
• reading more I find out that your answer is true (we will have a reverse current) if we are working with a permanent magnet, if the magnet field is generated by electromagnet, then it will be an inductor which will keep the current on the original direction, the current caused by the inductor is "stronger" then the reverse current Feb 24, 2017 at 12:51

I think I found an answer for all my doubts and I am sharing it here:

According to this video: https://www.youtube.com/watch?v=5mf4NmmLWnE when the the battery to the motor is on, and the armature is spinning we have both rules (right and left hand) acting simultaneously.

The right hand rule "generates a current" (actually a voltage) in the opposite direction of the applied voltage by the battery, but it is weaker then the battery and the resultant voltage is positive (thus keeping the current going forward and not reverse). This is called back emf.