SAT Subject Physics Practice Question 103: Answer and Explanation

Next steps

Question: 103

3. The figure below shows a small circular loop of wire in the plane of a long, straight wire that carries a steady current I upward. If the loop is moved from distance x2 to distance x1 from the straight wire, what will be the direction of the induced current in the loop and the direction of the corresponding magnetic field it produces?

A. The induced current will be clockwise, and the magnetic field it produces will point out of the plane of the page.
B. The induced current will be clockwise, and the magnetic field it produces will point into the plane of the page.
C. The induced current will be counterclockwise, and the magnetic field it produces will point out of the plane of the page.
D. The induced current will be counterclockwise, and the magnetic field it produces will point into the plane of the page.
E. None of the above

Correct Answer: C

Explanation:

To the right of the long straight wire, the magnetic field points into the plane of the page, and it is stronger at x1 than at x2. This means that the “into-the-page magnetic flux” through the loop increases as the loop is moved from x1 to x2. Since the flux is into the page and increasing, Lenz’s law says that the current induced in the loop will be counterclockwise to produce its own out-of-the-page magnetic flux.

Previous       Next