Mathematics > EXAM > AP PHYSICS C: ELECTRICITY AND MAGNETISM Unit 13 Part 1 (All)

AP PHYSICS C: ELECTRICITY AND MAGNETISM Unit 13 Part 1

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Clements H S CALC 466 A closed cylinder has a circular face on each end with an area . How are the area vectors of the circular faces defined? (A) Each face has a single area vector perpendicular to the plane of the surface and directed outwards from the cylinder. (B) Each face has a single area vector perpendicular to the plane of the surface and directed inwards towards the cylinder. (C) Each face has a single area vector parallel to the surface of the cylinder. (D) Each face has two area vectors parallel to the surface but perpendicular to each other. Answer A Correct. The area vector is defined to be perpendicular to the plane of the surface and directed outward from a closed surface. AP PHYSICS C: ELECTRICITY AND MAGNETISM Scoring Guide unit 13 part 1 AP Physics C: Electricity and Magnetism Page 1 of 47 2. A bar magnet of length moving at a constant velocity passes through points , , and . The north pole of the magnet moves parallel to and a distance in front of the plane of a stationary conducting rectangular loop. The bar magnet is aligned with the center of the loop at Point and is equal distances on either side of the loop at points and . Which of the following correctly describes the directions of the current in the loop as the magnet reaches and passes through the indicated points? Current at Point Current at Point Current at Point A Clockwise Counterclockwise B Counterclockwise Clockwise C Clockwise D Counterclockwise (A) A (B) B (C) C (D) D Answer B Correct. The magnetic field points into the page through the loop. As the magnet enters the loop at Point , the magnetic flux increases. By Lenz’s law and a right-hand rule, the induced current must be counterclockwise to produce an opposing magnetic field. The opposite happens as the magnet moves out of the loop as at Point . At the instant the magnet is centered, the rate of change in the flux is zero and therefore there is no current. Scoring Guide unit 13 part 1 Page 2 of 47 AP Physics C: Electricity and Magnetism 3. A conductive loop is attached to a cart that moves with a constant velocity through a region of constant magnetic field directed out of the page, as shown. What is the direction of the current in the loop as the cart exits the field, and why? (A) Clockwise, because the flux through the loop is decreasing, inducing a current in the loop that produces a magnetic field out of the page. (B) Clockwise, because the flux through the loop is increasing, inducing a current in the loop that produces a magnetic field into the page. (C) Counterclockwise, because the flux through the loop is decreasing, inducing a current in the loop that produces a magnetic field out of the page. (D) Counterclockwise, because the flux through the loop is increasing, inducing a current in the loop that produces a magnetic field into the page. Answer C Correct. The flux is decreasing. The induced current will produce a magnetic field to counteract the change in the flux. A right-hand rule gives that a current that produces a magnetic field that points out of the page is counterclockwise.

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