How to determine the polarities of inductor?

I know it is determined from Lenz law but most of the time i get a wrong answer,can anyone demonstrate how it is got, through an example?


1 Answer 1


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Suppose that the current though the coil is increasing.

This means that the magnetic field inside the coil is increasing.

Lenz tells you that the induced current will try and oppose the charge producing it which is the increasing current.

So the induced current must be in the opposite direction to the current producing the change, the increasing current.
So the induced current will be going out of the coil on the left-hand side and into the coil on the right hand side.

So as far as the circuit outside the coil is concerned due to the induced current the right hand end of the coil is negative and the left hand end is positive.

  • 1
    $\begingroup$ i understood how to predict the direction of current but i couldn't understand the polarities part,how is the current going from lower potential to higher potential inside the coil? $\endgroup$ Feb 26, 2016 at 9:42
  • $\begingroup$ Inside a battery a chemical reaction drives current from the negative terminal of the battery to the positive terminal and outside the battery the current flows from the positive terminal to negative terminal. In the case of a coil with a changing current, inside the coil the induced current is driven by the change of magnetic flux from the negative terminal to the positive terminal whilst outside the coil the current flows from the positive terminal to the negative terminal. $\endgroup$
    – Farcher
    Feb 26, 2016 at 10:00

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