Chapter Assumptions
Unless stated otherwise, electromagnetic waves are assumed to be propagating as plane waves through a vacuum.When converting light-years to meters, assume that a year has 365 days.The speed of light in a vacuum is 3.00×10^8 m/s.The Sun radiates energy at the rate of 3.91×10^26 W.Chapter 30 Problems
Conceptual Problems
C.1 In a phenomenon called diffraction, waves are able to bend around obstacles. For example, ocean waves can bend around
a piling so that it does not cast a down-wave "shadow" of calm water. The shorter the wavelength of a wave, the less able it is
to diffract around obstacles. You have experienced this yourself: You cannot see the people in a room down the hall, but you
can hear them talking, corresponding to the fact that a typical wavelength of light is about ten million times shorter than that of
a typical sound. If you live near the big city, but behind a rather large mountain, which of the urban radio broadcasts are you
likely to receive the best: AM or FM? Explain.
AM FM
C.2 Half of all the electromagnetic radiation reaching the Earth from the Sun lies in the visible spectrum that can be perceived by
the human eye: ranging from extremes of 390 nm to 780 nm. This is a tiny portion of the whole electromagnetic spectrum, and
it can't be just a coincidence. Why is so much of the Sun's radiation visible?C.3 Clouds scatter light just as the atmosphere
does. Since clouds consist mainly of
microscopic water droplets of many sizes, they
scatter all the wavelengths of visible light
equally. The smallest droplets scatter the
shortest wavelengths at the violet end of the
spectrum, and larger droplets scatter light of
longer wavelengths. Since all wavelengths are
equally scattered by a cloud, it appears white.
So does a jet's condensation trail, or fog, or
steam, or mist on a window.
Well, not quite white. In fact if you look at a real (cumulus) cloud, you will see that parts of it appear bright white, while other
parts appear gray, and at the bottom of a thick cloud, almost black. What accounts for these variations?C.4 It is early morning, and the Sun is rising (where else?) in the east. (a) What is the direction of polarization of the skylight
directly overhead? (b) What is the direction of polarization of the skylight as you look toward the northern horizon?
(a) i. East-west
ii. North-south
(b) i. Vertical
ii. Horizontal
C.5 Now it is noon, and the Sun is directly overhead. (a) What is the direction of polarization of the skylight coming from the
eastern horizon? (b) What is the direction of polarization of the skylight as you look toward the northern horizon?
(a) i. Vertical
ii. Horizontal
(b) i. Vertical
ii. Horizontal
C.6 Sunlight which reflects off smooth surfaces like those of roadways or standing water becomes horizontally polarized in the
process. Polarizing sunglasses are designed to completely block this reflected glare, while at the same time they reduce the
intensity of unpolarized ambient light by one-half. (a) If a sunglasses lens is to block reflected glare, what should the
orientation of its transmission axis be? (b) LCD displays, such as flat panel computer display screens, and certainly
automobile instruments and digital writswatch faces, should be readable by people wearing polarized sunglasses. In order for
them to be readable, what should the transmission-axis orientation of their front "analyzer" filters be? (Note: The conceptual
diagrams of LCDs in the text may or may not have been drawn to reflect this requirement.)
(a) Vertical Horizontal
(b) Vertical Horizontal(^570) Copyright 2000-2007 Kinetic Books Co. Chapter 30 Problems