Induced current in long straight wire

[w3390]

Homework Statement

A current is induced in a loop by something happening with current in a long straight wire near the loop. What could be happening? (There are two possibilities. Neither the wire nor the loop is moving.)

Homework Equations

Ampere's Law
Faraday's Law

The Attempt at a Solution

I'm pretty sure I know one of the possibilities. I said that one possibility is that the current in the straight wire is changing. This changing current will create a magnetic field. This created magnetic field will then induce a current in the loop. I cannot think of the other possibility if the wire and loop are not moving. Any help would be appreciated.

 

[Dadface]

The only other possibility I can think of is that the straight wire is fed by a d.c. supply which is then switched on or off the current in the coil being induced at those instants.I do not like this answer, however, because the current does change momentarily during switching and you have already described a changing current.

 

[nlightner]

The other possibility could be that the loop is moving relative to the wire, causing a change in the magnetic flux through the loop. This change in magnetic flux will induce a current in the loop according to Faraday's Law. Another possibility is that the loop is made of a conducting material and is placed in the changing magnetic field created by the current in the straight wire. This changing magnetic field will induce an electric field in the loop, causing a current to flow. Both of these possibilities demonstrate the fundamental relationship between electricity and magnetism, known as electromagnetic induction.