As shown in the figure,a straight wire carries a steady current I.A metal bar is in contact with a pair of rails and is in upward motion with velocity of magnitude ν.The polarity of the induced emf in terminals X and Y is

Question

Quizplus · Accepted Answer

According to Faraday's law of electromagnetic induction, a changing magnetic flux induces an electromotive force (EMF) in a closed loop. In this case, the motion of the metal bar perpendicular to the magnetic field (which is directed into the plane of the paper) changes the magnetic flux through the loop formed by the metal bar and the rails.

Applying the right-hand rule for the direction of induced current, we find that the induced current flows counterclockwise as seen from above. This means that the induced magnetic field opposes the external magnetic field, which implies that the induced magnetic field is directed out of the screen.

Now, consider the orientation of the loop formed by the metal bar and the rails. The top of the loop is moving upward, which means that the induced current flows from Y to X through the metal bar. Since the current flows from the positive terminal to the negative terminal, we conclude that Y is positive and X is negative. Therefore, the correct choice is C, Y is positive and X is negative.

As Shown in the Figure,a Straight Wire Carries a Steady