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
E) V

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 
E) V

Quizplus · Accepted Answer

As the loop enters the region with uniform magnetic field, the magnetic flux through the loop begins to increase, inducing an EMF and therefore a current in the loop. This current will be at its maximum when the rate of change of flux is maximum, which occurs when the loop is fully inside the magnetic field. Graph III shows the current reaching a maximum as the loop enters the region of uniform B field, and then decreasing as the loop moves further into the field. The other graphs either do not show the current reaching a maximum or do not show the correct behavior as the loop enters the magnetic field.

A Square Loop of Wire Moves with a Constant Speed