Section Problems
Section 1 - The electromagnetic spectrum
1.1 The speed of light in a vacuum is exactly 299,792,458 m/s. This speed is sometimes used to provide a convenient yardstick
for large astronomical distances. (a) A light-second is the distance light travels in one second. If the Moon is 3.84×10^8 m from
the Earth (center to center), how many light-seconds away is it? (b) A light-minute is the distance light travels in one minute. If
the Earth is 1.50×10^11 m from the Sun, how many light-minutes away is it? (Your answer also represents the number of
minutes it takes for light to reach the Earth from the Sun.) (c) A light-year is the distance light travels in one year. The Sun is
28,000 light-years from the center of the Milky Way galaxy. What is this distance in meters?
(a) light-seconds
(b) light-minutes
(c) m1.2 Nowadays many highway tunnels are equipped with AM "repeaters" so that motorists can listen to their AM radios while
inside. Otherwise, AM radio cannot be received in the tunnel. FM repeaters are not usually necessary, since FM reception in
tunnels is often acceptable without any special assistance. A typical tunnel is 5 meters high. (a) What is the wavelength of the
electromagnetic radiation from an FM station broadcasting at 94.1 MHz, which penetrates easily into the tunnel? (b) What is
the wavelength of the electromagnetic radiation from an AM station broadcasting at 940 kHz, which ordinarily cannot
penetrate into the tunnel?
(a) m
(b) m1.3 A certain radio station broadcasts electromagnetic radiation with a wavelength of one quarter mile (0.25 mi). (a) What is the
frequency of the broadcast? (b) Is the station AM or FM?
(a) Hz
(b) AM FM1.4 The color to which the human eye is most
sensitive is a yellowish green with a
wavelength of approximately 550 nm. (For this
"scientific" reason there was a brief vogue in
the 1980s for making fire trucks this color, a
fad that faltered when departments found that
firefighters took little pride in non-red fire
trucks and consequently maintained them
poorly. In fact, the photographer of the
accompanying picture was told that the truck
will be painted red "within a month í red is
traditional".) (a) What is the frequency of waves of this color? (b) How many wavelengths of this yellowish green light are
there in the thickness of a human hair that is 110 ȝm in diameter? (c) How many wavelengths of the light are there in the
width of a pencil, 6.00 mm?
(a) Hz
(b)
(c)1.5 The rather unappetizing confection you see in
the photograph is a carrot strip that has been
cooked in a microwave oven from which the
rotating turntable was removed. When it is
turned on, the oven uses a "magnetron" tube
to generate standing microwaves in the cavity
of the oven. No cooking heat is generated at
the locations of the standing-wave nodes, and
maximal heat (microwave "hot spots") is
generated at the locations of the standing-
wave antinodes. The manufacturer's label on
the oven states that it operates at a frequency of 2450 MHz. (a) Based on this frequency, what is the wavelength of the
microwaves generated inside the oven? (b) Based on your answer to part a, what is the distance between two antinodes of
the standing microwaves? Give your answer to three significant figures. (c) Is the result in part b compatible with the
measurement shown in the photograph?
(a) cm (b) cm (c) Yes No