FIGURE 23-3
-The wire in Figure 23-3 carries a current I that is decreasing with time at a constant rate. The induced emf in each of the loops is such that
A) no emf is induced in any loop.
B) all loops experience counterclockwise emf.
C) loop A has clockwise emf, loop B has no induced emf, and loop C has counterclockwise emf.
D) loop A has counterclockwise emf, loop B has no induced emf, and loop C has clockwise emf.
E) loop A has counterclockwise emf, loop B clockwise emf, and loop C has clockwise emf.

Question

FIGURE 23-3 
-The wire in Figure 23-3 carries a current I that is decreasing with time at a constant rate. The induced emf in each of the loops is such that
A) no emf is induced in any loop. 
B) all loops experience counterclockwise emf. 
C) loop A has clockwise emf, loop B has no induced emf, and loop C has counterclockwise emf. 
D) loop A has counterclockwise emf, loop B has no induced emf, and loop C has clockwise emf. 
E) loop A has counterclockwise emf, loop B clockwise emf, and loop C has clockwise emf.

Quizplus · Accepted Answer

According to Faraday's Law, a changing magnetic flux through a loop induces an emf in that loop. The direction of the induced emf is such that it opposes the change in flux. In this case, the decreasing current in the wire creates a decreasing magnetic field, which in turn creates a decreasing magnetic flux through each loop. To oppose this change, each loop must produce an emf that creates a magnetic field that opposes the original field. Applying the right-hand rule for electromagnetic induction, we find that loop A has a counterclockwise induced current, loop B has no induced current (since it is perpendicular to the magnetic field and its area is not changing), and loop C has a clockwise induced current. Thus, the correct choice is D.

FIGURE 23-3 -The Wire in Figure 23-3 Carries a Current I That