Question

At a certain location there is a constant horizontal magnetic field pointing to the east. A square loop of wire is placed in this field. At time A the bottom of the loop is resting on the floor (which is insulating), and the plane of the square loop is vertical and perpendicular to the magnetic field. The loop tips over and at time B it is flat on the floor. For this situation...

A) Before the loop starts to tip over, the induced current is flowing southward through the bottom side of the square

B) The magnetic flux is greatest before the loop tips over

C) Current is induced to flow in the loop because the magnetic field is changing

D) While the loop is tipping over, there is induced current flowing through the loop

E) The induced current is greatest just before the loop starts to tip

Answer 1

Current flows due to induced emf which is further due to changing magnetic flux. Magnetic flux depends on the magnetic field, the area of the loop and the angle between the two. Here the magnetic flux nd areaa of magnetic field is constant. The only thing that varies is the angle. Before the loop starts to tip over, no current will flow as flux at that instant is constant. Hence A and E are incorrect. C is also incorrect as the current is induced due to change in the angle between B and Area and B is constant. B is correct as in the initial position, maximum magnetic field lines cut through the area. We can also understand it mathematically. The magnetic flux is proportional to the Cos (Cosine) of the angle between B and A. In the initial position the angle is zero. As, Cos(0^o) = maximum, magnetic flux is maximum. Lastly, D is also correct as already discussed.