Chapter 25: Electromagnetic WavesAnswers to Even-Numbered Conceptual Questions2. 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 headingrelative 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.Solutions to Problems and Conceptual Exercises1. Picture the Problem: The electric field in an electromagnetic wave is increasing in magnitude at a particular time.Strategy: Use the connection E = cB (equation 25-9) between the magnitude of the electric field and the magnitude of the magnetic field in an electromagnetic wave in order to answer the conceptual question.Solution: The magnitudes of the electric and magnetic fields are connected to each other by E = cB (equation 25-9). Therefore, when the electric field is increasing, the magnetic field is increasing at the same time.Insight: The polarizations of the two waves are also linked. If the polarization direction of the electric field of an electromagnetic wave were rotated by 30°, the magnetic field direction also rotates by 30° in the same direction so that it is always perpendicular to the direction of the electric fied.2. Picture the Problem: The figure shows the electric field in the positive y direction and the magnetic field in the positive z direction.Strategy: Use the Right-Hand Rule (RHR) to determine the direction of propagation. Point the fingers of your right hand in the direction of the electric field.Bend them in the direction of the magnetic field. Your thumb points in the direction of the wave propagation.Solution: According to the RHR, the wave is traveling in the positive x direction .Copyright © 2010 Pearson Education, Inc. All rights reserved. This material is protected under all copyright laws as they currently exist. Noportion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher.25 – 1Chapter 25: Electromagnetic Waves James S. Walker, Physics, 4th EditionInsight: If the magnetic field had been in the positive x direction with the same electric field, the wave would propagatein the negative z direction.Copyright © 2010 Pearson Education, Inc. All rights reserved. This material is protected under all copyright laws as they currently exist. Noportion of this material may be reproduced, in any form or by any means, without permission in writing from the publisher.25 – 2Chapter 25: Electromagnetic Waves James S. Walker, Physics, 4th Edition3. Picture the Problem: A person on the positive y-axis observes an electromagnetic wave that radiates from an electric charge that oscillates sinusoidally about the origin and along the x-axis.Strategy: In order for the radiation to reach the person, it must propagate in the positive y direction (toward the person).The electric field will oscillate in the same direction as the charge. The magnetic field will oscillate perpendicular to the electric field and perpendicular to the direction of propagation.Solution: 1. (a) The electric field will oscillate in the x direction .2. (b) The magnetic field will oscillate in the z direction.3. (c) The electromagnetic wave will propagate in the positive y direction.Insight: If the person were standing on the z-axis, and at some instant the electric field were in the +x direction, the magnetic field would be in the +y direction, as the wave propagated in the positive z direction.4. Picture the Problem: A person on the positive y-axis observes an electromagnetic wave that radiates from an electric charge that oscillates sinusoidally about the origin and along the z-axis.Strategy: In order for the radiation to reach the person, it must propagate in the positive y direction (toward the person). The electric field will oscillate in the same direction as the charge. The magnetic field will oscillate perpendicular to the electric field and perpendicular to the direction of propagation.Solution: 1. (a) The electric field will oscillate in the z direction .2. (b) The magnetic field will oscillate in the x direction.3. (c) The electromagnetic wave will propagate in the positive y direction.Insight: If the person were standing on the positive x-axis, and at some instant the electric field were in the +z direction,the magnetic field would be in the −y direction, as the wave propagated in the positive x direction.5. Picture the Problem: The table shows the direction of propagation, direction of the electric field, and/or the direction of the magnetic field for four electromagnetic waves.Strategy: For each of the waves use the Right-Hand Rule to determine the missing information. Point the fingers of your right hand in the direction ofthe electric field, bend them in the direction of the magnetic field, and then your thumb will point in the direction of the wave propagation. If the electric field or magnetic field is unknown, guess the direction to see if your thumb points in the correct direction of propagation.Solution: 1. (a) The magnetic field