A square loop of wire moves with a constant speed v from a field-free region into a region of uniform B field, as shown.Which of the five graphs correctly shows the induced current i in the loop as a function of time t?
A)I
B)II
C)III
D)IV

Question

A square loop of wire moves with a constant speed v from a field-free region into a region of uniform B field, as shown.Which of the five graphs correctly shows the induced current i in the loop as a function of time t? 
A)I 
B)II 
C)III 
D)IV

Quizplus · Accepted Answer

As the loop enters the region with a uniform magnetic field, there will be a changing magnetic flux through the loop, which induces an EMF in the loop. This EMF will create a current in the loop, which will be at maximum when the loop is fully inside the magnetic field and decreasing as it exits the field. Graph III shows this behavior, with a sharp increase in current when the loop enters the field, and a gradual decrease as it exits. The other graphs do not show this behavior or show incorrect behavior, such as a constant current or a current that increases as the loop exits the field.

A Square Loop of Wire Moves with a Constant Speed