I am working with the Problem which I've seen in a book. That Problem was : https://physics.stackexchange.com/questions/227582/direction-of-induced-current

I can't find any meaningful explanation for this problem in any source. So, I am working with this problem. The answer of the first question is No Current is induced in the chord between the loop. And the Answer of the second question is No Current induced in connector. And in all the current is in clockwise direction.

Here, I have many questions regarding Electromagnetic Induction, and I don't think any theory provides its answer. If there is a theory please help me. I am a 12th grade student but cannot find the answer of these questions.

In my efforts to answer these problem,

  • I am confused how to apply lenz's law here?

  • Sudden Question arises, why Current or EMF is not generetad in unclosed wire. I know Maxwell's equation is defined on closed integral, but it doesn't means that unclosed wire don't generate current and emf.

  • If we are not going to apply Lenz's law, we should take interest in Induced Electric Field. (Maybe Electric field is zero in that connectors. But How?)

I 've read Halliday, Rennik, Walker's Fundamental Physics extended on Google books. But still confused about Induced electric field. How Symmetry implies Direction of Induced Electric field is tangential.

I know I've many questions and should not type it here together. But My main question is to find the direction of induced current in the figure given in the link.

  • Another Question is what about induced emf and induced current in a circuit rather than a loop? Are there any answers?

1 Answer 1


First realise that you can induce an emf in any closed loop. Only if the loop is conducting do you get an induced current.

The direction of the induced current will always be in such a direction of oppose the change producing it.

Here is a relatively simple way of assigning an induced current

enter image description here

Diagram 1 There is a loop with a decreasing B-field into the screen.

Diagram 2 Lenz tells you that the induced current must try and counteract that decreasing B-field into the screen by producing a B-field out of the screen.

Diagram 3 Use the right hand grip rule to assign the direction of the current.

Now your problems require a bit more thought eg as to how to deal with the link between the outer and inner ring in the left hand diagram. I suggest you apply Lenz to each of the semicircles and see what you get.

You can do an great deal with these simple ideas and you do not need to go back all the way to Maxwell.

So for your first question see what Lenz predicts for these three loops.

enter image description here

  • $\begingroup$ Please Explain How I apply Lenz to each diagram. I am just confused whether I am right or wrong. $\endgroup$ Feb 1, 2016 at 12:25
  • $\begingroup$ Do you mean the diagrams in your problem? $\endgroup$
    – Farcher
    Feb 1, 2016 at 12:56
  • $\begingroup$ Yeah. Do you mean current in opposite directions will vanish by themselves? $\endgroup$ Feb 1, 2016 at 13:05
  • $\begingroup$ If you think that the currents and equal in magnitude but opposite in direction then yes the current is zero. $\endgroup$
    – Farcher
    Feb 1, 2016 at 13:08
  • $\begingroup$ What is actual phenomenon on micro level then ? What happens to electrons flowing in the conductor ? They repel each other ? $\endgroup$ Feb 1, 2016 at 13:11

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