Chapter Assumptions
Unless stated otherwise, use 5.00×10–5 T for the strength of the Earth's magnetic field at its surface.
Elementary charge, e = 1.60×10–19 C
Chapter 29 Problems
Conceptual Problems
C.1 The textbook displays a photograph of an experiment where a bar magnet is dropped through a coil of wire. The changing
magnetic flux through the coil induces an emf that in turn drives a current through the wire. The emf is displayed on an
oscilloscope. After the magnet goes through the coil does it hit the pillow with the same kinetic energy as it would if there were
no coil? Explain.
Yes No
C.2 A large spool holding a coil of hundreds of loops of telephone cable is loaded on a truck at the factory in New York, and
transported to a utility in Georgia. During the trip, a meter which is attached to the coil registers a tiny intermittent current in
the coil. If there is no battery attached to the coil, what is the cause of the current?C.3 A circular loop of wire is located in a constant, uniform magnetic field. How can an emf be induced in the loop?C.4 A wire loop lies in the xy plane. A magnetic field points in the positive z direction. If the radius of the loop begins to shrink, in
what direction will the current in the loop flow? Give your answer from the perspective of looking down on the xy plane, and
explain your answer.Clockwise Counterclockwise
C.5 Suppose you are looking down on a wire loop, perpendicular to the plane it lies in. A magnetic field is pointed toward you and
is increasing in strength. Will the induced current flow clockwise or counterclockwise? Explain your answer.
Clockwise Counterclockwise
C.6 "Superman - The Escape" is a thrill ride at Six Flags Magic Mountain in Valencia, CA. A 3000 kg car is accelerated to a
height of over 100 meters. On the return trip the car is brought to a stop using electromagnets which induce eddy currents in
the large wheels of the car. Since energy must be conserved, where does the nearly three million joules of gravitational
potential energy go?C.7 Carefully observe the animation of the swinging block in the textbook. (a) What is the direction of the eddy currents when the
block swings into the magnetic field? (b) What is the direction of the eddy currents when the block swings out of the magnetic
field? (c) Explain your answer to part a using Lenz's law.
(a) Clockwise Counterclockwise
(b) Clockwise Counterclockwise
(c)
C.8 The poles of a powerful magnet are oriented to oppose one another, with a gap in between them, so that the field lines from
the north to the south pole are horizontal. You drop a copper penny so that it falls through the gap. (a) Describe what happens
to the acceleration of the penny as it passes between the poles. (b) The effect described in part a would be different for a coin
like a dime, which is close to the size and weight of a penny, but is made of a metal with a different resistivity. Describe a
practical application of this difference in the coins, in a type of machine you have probabaly used.
(a)
(b)
C.9 We have seen that it is possible for a changing current in one loop to cause a current to flow in an adjacent loop. (a) If the
loops are lying flat on a surface, side by side, and the current in the first loop suddenly increases, does the induced current in
the second loop flow in the same direction (by "direction" we mean clockwise or counterclockwise) as the original current, or
in the opposite direction? Explain your answer. (b) Describe a configuration for the two loops which gives the opposite result.
(a) The same direction The opposite direction
(b)Section Problems
Section 0 - Introduction
0.1 Use the simulation in the interactive problem in this section to answer the following questions. (a) Will a current flow in the
bottom circuit if the current in the top circuit is steady and unchanging? (b) Is there current in the bottom circuit if the current in