In this question, I easily understand the solution. But I want to determine the direction of induction current (I inc) with the Lenz Law. I know how works Lenz Law, but I couldn't determine the direction of I inc.

Also, something unclear with the solution is polarities of the V emf. How did we choose the polarities?



  • \$\begingroup\$ Current isn't induced; voltage is induced; current flows as a result of that induced voltage and the conduction path. \$\endgroup\$ – Andy aka Dec 13 '18 at 10:50
  • \$\begingroup\$ @Andyaka Then how to choose polarities (+/- points) of induced voltage? \$\endgroup\$ – Erdem Uysal Dec 13 '18 at 19:45

The induced voltage generates a current and resultant magnetic field that opposes motion. Therefore, the induced field must make the resultant total magnetic field stronger to the right of the moving conductor and weaker to the left (opposing force on the conductor is from a stronger field to a weaker field).

Therefore the circular field around the moving conductor must be up to its right so down to its left, and the current is from 1 to 2 through the conductor and from 2 to 1 through the resistor. Hence the negative sign in your derived equation for induced emf.


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