When the current in the long wire is turned off, the magnetic field created by the wire will decrease. This decrease in the magnetic field will reduce the flux in the nearby loop, which will produce an induced current according to Faraday’s Law of Electromagnetic Induction. When there is an electric current in both the wire and loop, there is a force between the two.
Let the current in the long wire at some instant be I.
To complete the solution, we need to know the force between a long current-carrying wire and a current-carrying loop. Let us find that.
The force between the wire and the loop can be obtained by finding the force due to wire on each arm AB, BC, CD and DA separately.
The force on the arms BC and DA will cancel each other as the magnitudes are equal and direction opposite....