2 . A uniform magnetic field B points up the page, as shown above. A loop of wire carrying a clockwise
current is placed at rest in this field as shown above, and then let go. Which of the following
describes the motion of the wire immediately after it is let go?
(A) The wire will expand slightly in all directions.
(B) The wire will contract slightly in all directions.
(C) The wire will rotate, with the top part coming out of the page.
(D) The wire will rotate, with the left part coming out of the page.
(E) The wire will rotate clockwise, remaining in the plane of the page.
3 . An electron moves to the right in a uniform magnetic field that points into the page. What is the
direction of the electric field that could be used to cause the electron to travel in a straight line?
(A) down toward the bottom of the page
(B) up toward the top of the page
(C) into the page
(D) out of the page
(E) to the left
Free Response:
4 . A circular loop of wire of negligible resistance and radius R = 20 cm is attached to the circuit shown
above. Each resistor has resistance 10 Ω. The magnetic field of the Earth points up along the plane of
the page in the direction shown, and has magnitude B = 5.0 × 10−5 T.
The wire loop rotates about a horizontal diameter, such that after a quarter rotation the loop is no
longer in the page, but perpendicular to it. The loop makes 500 revolutions per second, and remains
connected to the circuit the entire time.
(a) Determine the magnetic flux through the loop when the loop is in the orientation shown.
(b) Determine the maximum magnetic flux through the loop.
(c) Estimate the average value of the induced EMF in the loop.