enter image description here

So I have a loop, in a magnetic field directed into the plane that the loop is lying in as shown in the figure. Let's assume that the loop is being moved towards right with uniform velocity.

Question: In which direction would this movement produce current in the loop?

I know about the Lenz's law, but I don't understand how I can apply it to this. Like what would be the way in which current induced in the loop would oppose the magnetic field it is present in.

I am familiar with the thumb rule, wrap right hand fingers along a wire with the thumb pointing in direction of current and the curl of fingers give the direction of magnetic field it produces.

I do not think that this rule can be used here.

If you have an assumption that would clarify this in a better manner then please do use that.


1 Answer 1


From your question, it seems like the magnetic field is not changing. For current to get induced in loops, Magnetic flux through the area of the loop has to vary with respect to time. Just placing the conducting loop at rest in a constant magnetic field will not induce any current in the loop.
Even if the loop is moved towards the right(with any speed) it still does not change the magnetic flux passing through the area enclosed by the loop.
But if the magnetic field is limited to an extent, and the loop is being pulled out of the field in the right, then there is a change in the field as the field that was present before in the part that is out of the field now, is no more present. And this can be assumed as decrease in magnetic field in the downward direction.
So, to oppose the decrease in the magnetic field in the downward direction, the loop itself induces a magnetic field in the downward direction trying to neutralize the decrease in the magnetic field.
So point your right-hand thumb down and curl your fingers,
Induced current through the loop is in the clockwise direction.
Note: Downward direction means into the plane of the paper.

  • $\begingroup$ Yes I realized, fixed it. $\endgroup$
    – Arkilo
    Jul 16, 2019 at 19:00
  • $\begingroup$ @Arkilo, I Edited the answer. $\endgroup$
    – MrVajid
    Jul 16, 2019 at 19:15
  • 1
    $\begingroup$ I see, so in the case the magnetic field is directed outside the plane of paper, I assume given this same case of being 'pulled out' of the field, the loop will now induce a magnetic field in the upward direction to make up for the loss and the direction of current will be anti clockwise. $\endgroup$
    – Arkilo
    Jul 16, 2019 at 19:22
  • $\begingroup$ Yes, you got it right. When the magnetic flux through a loop changes, a current is induced in the loop such that the magnetic field due to the induced current opposes the change in magnetic flux through the loop. $\endgroup$
    – MrVajid
    Jul 16, 2019 at 19:25
  • $\begingroup$ Thanks man, very cool. $\endgroup$
    – Arkilo
    Jul 16, 2019 at 19:27

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