A rectangular coil moving at a constant speed v enters a region of uniform magnetic field from the left. While the coil is entering the field on the left, the direction of the current through the right side of the loop is
A) 1.
B) 2.
C) 3.
D) 4.
E) 5.

Question

A rectangular coil moving at a constant speed v enters a region of uniform magnetic field from the left. While the coil is entering the field on the left, the direction of the current through the right side of the loop is
A) 1. 
B) 2. 
C) 3. 
D) 4. 
E) 5.

Quizplus · Accepted Answer

According to Faraday's law of electromagnetic induction, the magnetic field induces an emf in the coil, which causes a current to flow. The direction of the induced current is given by Lenz's law, which states that the induced current flows in a direction that opposes the change in magnetic flux that produced it. As the coil enters the region of the magnetic field from the left, the magnetic flux through the coil increases, and thus the induced current flows in a direction that creates a magnetic field that opposes the external magnetic field on the left side of the coil. Therefore, the right side of the coil must have a current flowing in the direction opposite to choice 2 and choice 3, but in the same direction as choice 1 and choice 5. However, since the coil is moving to the right, the induced current lags behind the change in magnetic flux, and thus the current in the right side of the coil must flow in the direction of the external magnetic field, as in choice 4.

A Rectangular Coil Moving at a Constant Speed V Enters