Answer
See explanation.
Work Step by Step
By Lenz’s Law, the field caused by the induced current is directed to oppose the change in flux.
The magnetic field due to I is out of the page for loops A and C. It is into the page for loops B and D. The field is constant since the current is constant. Any magnetic flux change is because the loops are moving.
a.
A: The loop is moving away from the wire, so the magnetic field it sees, directed out of the page, is getting weaker. The induced current flows in a direction so to make more magnetic field that is out of the page. By the right hand rule, this is counterclockwise.
B: The loop is moving away from the wire, so the magnetic field it sees, directed into the page, is getting weaker. The induced current flows in a direction so to make more magnetic field that is into the page. By the right hand rule, this is clockwise.
C: The flux through the loop is constant. There is no induced current.
D: The loop is moving toward the wire, so the magnetic field it sees, directed into the page, is getting stronger. The induced current flows in a direction so to make magnetic field that is out of the page. By the right hand rule, this is counterclockwise.
b.
A: The flux is decreasing. The loop is pulled toward the wire, which tends to increase the flux.
B: The flux is decreasing. The loop is pulled toward the wire, which tends to increase the flux.
C: There is no force.
D: The flux is increasing. The loop is repelled from the wire, which tends to decrease the flux.
In part b, to confirm our answers, we could also look at the direction of the force on the part of each loop that is closest to the straight wire.
