Download Chapter 22: Magnetism

Chapter 22: Magnetism
Answers to Even-Numbered Conceptual Questions
2.
Yes. If an electric field exists in this region of space, and no magnetic field is present, the electric field will
exert a force on the electron and cause it to accelerate.
4.
In a uniform electric field the force on a charged particle is always in one fixed direction, as with gravity near
the earth's surface, leading to parabolic trajectories. In a uniform magnetic field the force of a charged particle
is always at right angles to the motion, resulting in circular or helical trajectories. Perhaps even more
important, a charged particle experiences a force due to an electric field whether it is moving or at rest; in a
magnetic field, the particle must be moving to experience a force.
6.
A current-carrying wire in a uniform magnetic field can experience zero force only if the wire points in the
same or opposite direction as the magnetic field. In such a case, the angle θ in equation 22-4 will be either 0˚
or 180˚, in which case F = ILB sinθ = 0.
Chapter 23: Magnetic Flux and Faraday’s Law of Induction
Answers to Even-Numbered Conceptual Questions
2.
The magnetic field will have little apparent effect, because the break in the ring will prevent a current from
flowing around its circumference. What the magnetic field will do, however, is produce a nonzero emf
between the two sides of the break.
4.
The metal plate moving between the poles of a magnet experiences eddy currents that retard its motion. This
helps to damp out oscillations in the balance, resulting in more accurate readings.
6.
Nothing. In this case, the break prevents a current from circulating around the ring. This, in turn, prevents the
ring from experiencing a magnetic force that would propel it into the air.
8.
As the penny begins to tip over, there is a large change in the magnetic flux through its surface, due to the
great intensity of the MRI magnetic field. This change in magnetic flux generates an induced current in the
penny that opposes its motion. As a result, the penny falls over slowly, as if it were immersed in molasses.
10.
When the angular speed of the coil in an electric generator is increased, the rate at which the magnetic flux
changes increases as well. As a result, the magnitude of the induced emf produced by the generator increases.
Of course, the frequency of the induced emf increases as well.
12.
When the switch is opened in a circuit with an inductor, the inductor tries to maintain the original current. (In
general, an inductor acts to resist any change in the current—whether the current is increasing or decreasing.)
Therefore, the continuing current may cause a spark to jump the gap.
Chapter 25: Electromagnetic Waves
Answers to Even-Numbered Conceptual Questions
2.
We can tell if a weather system is approaching or receding by noting if the frequency of the reflected radar
beam has been shifted up or down. The system is approaching if the frequency is higher; it is receding if the
frequency is lower.
4.
Light reflected from a horizontal surface has a polarization in the horizontal direction. It follows that when
you sit upright, with the transmission axis of your glasses in the vertical direction, they will block most of the
reflected light. When you lie on your side, however, the transmission axis is horizontal. This allows most of
the reflected light to enter your eyes.
6.
The light from the sky is polarized at right angles to the direction of the Sun; therefore, the amount of light
received by each of the two polarizing eyes will depend on the orientation of the spider relative to the Sun. By
monitoring the amount of light received by each eye, the spider can maintain a course on a given heading
relative to the Sun.
8.
View the light reflected from a horizontal surface, such as a tabletop. This light is polarized primarily in the
horizontal direction. Therefore, if you rotate the sheet of polarizing material until you receive a maximum
amount of reflected light, you will know that its transmission axis is horizontal.
10.
As mentioned in the answer to conceptual question 4, the light reflected from a horizontal surface is polarized
primarily in the horizontal direction. If the glasses are merely tinted, reflected light will have the same
intensity no matter how the glasses are rotated. If they are Polaroid, however, you will notice a striking
difference in reflected intensity as you rotate the glasses.