A flat loop & a long wire lie in the same plane.?

Question

If the current in the wire decreases suddenly, in which sense(clockwise / counterclockwise) is the induced current in the loop?

Answer 1

I think you need a diagram, because the answer depends on which side the loop is, and which way the current in the wire is flowing.  

But, the way to solve using Lenz law, which says that in a loop the magnetic flux wants to stay constant.  So, if you have current flowing in a wire, you have a magnetic field circling around using the right-hand rule.  So, suppose current is flowing up in the wire, and the loop is to the right of the wire, as so:

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then then nominal magnetic flux is pointing into the page.  You use the right hand rule -- point thumb in direction of current, then curl fingers around in direction of magnetic field.

Now, if the current decreases, then the flux into the loop from the wire decreases ... which the loop does not like, so it creates its own current to try to increase the flux into the page.

Again, you use the right hand rule (this time pointing thumb along loop -- you want your fingers to curl into the page, to make up for the decreasing flux into the page.

Obviously the answer will flip if the current was heading down originally, or if the loop was on the left side.