Quiz 2: Solutions
1 1 Across: angular
3 Across: spectrum
6 Across: proper
7 Across: nebula
8 Across: dopplershift
13 Across: elliptical
14 Across: telescope
15 Across: planet
16 Across: orion
17 Across: galileo
18 Across: lightyear
2 Down: nanometer
3 Down: speedoflight
4 Down: electromagnetic
5 Down: astronomicalunit
6 Down: parallax
9 Down: infrared
10 Down: frequency
11 Down: spectroscopy
12 Down: wavelength
2
Astronomers refer to the distance that light travels in one year as
(Solution: Consult Chapter 2. A light year is defined to be the distance that light travels in one year.)
a. one
year.
3
b. one
ecliptic.
c. one
mile.
d. one
light
year.
e. You can't fool me, astronomers have no
specific term that is defined to be the
distance that light travels in one year!
The star Betelgeuse is the bright red star in the constellation of Orion (see color figure 5 on page 3 of the "Color Gallery 1" in your
textbook). It is the estimated to be 500 light years (LY) away from Earth. Suppose that right now, Betelgeuse explodes as a
supernova. In what year would people on Earth first become aware that Betelgeuse had exploded?
(Solution: Consult textbook Chapter 2. Since the light from Betelgeuse takes 500 years to reach us, we would not know that the
star had exploded for another 500 years. Thus, we would learn that Betelgeuse had exploded about 500 years from now, or
the year 2511.)
a. Sometime in the year 2012 (i.e., in about 500
days from today).
d. In 2511 (i.e., in about 500 years from now).
b. In the year 2011 (i.e., we would learn about
Betelgeuse exploding right away).
e. About 1511 (i.e., we would have already learned of
Betelgeuse's demise about 500 years ago).
c. In 2111 (i.e., about 100 years from now).
4
When you solve the following algebraic equation for x , what value do you get?
4x + 3 = 11
(Solution: Consult the Mathematical Toolkit. Following the algebra rules given in the Mathematical Toolkit, to solve for x we start
by subtracting 3 from both sides of the equation, to yield:
4x = 8
Next, we divide both sides by 4, to yield:
x= 8
4
Or, put more simply:
x=2
Which is our final answer.)
a. x=4
5
b. x=0
c. x=2
d. x=3
e. None of the above are the correct value of x
The Sun's radius is roughly 100 times that of the Earth. Assuming both the Sun and Earth to be spheres, about how many times
larger is the Sun's circumference than that of the Earth?
(Solution: Consult Mathematical Toolkit. Following exactly the procedure outlined in the mathematical toolkit:
rSun = 100rEarth
Circumference = 2 r
The ratio of the Sun's circumference to Earth's circumference is therefore:
circumference of Sun = 2 rSun
circumference of Earth 2 r
Earth
Canceling common factors and substituting yields:
circumference of Sun = 100 .
circumference of Earth
1
Thus, the circumference of the Sun is 100 times larger than the circumference of the Earth.)
a. The Sun's circumference is
2 100 times larger than that of
the Earth.
..to be continued
c. The Sun's circumference is 10
times larger than that of the
Earth.
e. The Sun's circumference is
the same as that of the Earth.
continuation
b. The Sun's circumference is 100 times larger than
that of the Earth.
6
d. The Sun's circumference is 2 that of the Earth.
times larger than
When you solve the following algebraic equation for x , what value do you get?
4x + 2 = 7
2
(Solution: Consult the Mathematical Toolkit, and associated web pages. Here's how to solve it:
4x + 2 = 7
2
So, the whole point is to get that "x" on the left hand side all alone.
To do this, begin by multiplying both sides by 2 to eliminate the 2 in the denominator on the left hand side:
4x + 2 x 2 = 7 x 2
2
4x + 2 = 14
Now, subtract 2 from both sides to eliminate the 2 on the left hand side:
4x + 2 2 = 14 2
4x = 12
Now, divide both sides by 4 to eliminate the 4 on the left hand side.
4x = 12
4
4
x= 3
And that's the answer! x = 3.)
a. 1/3
7
b. 4/7
c. 7/4
d. 3
e. 9
The Sun's radius is roughly 100 times that of the Earth. Assuming the Earth and Sun to be spheres, about how many times larger
is the Sun's surface area than that of the Earth?
(Solution: Consult Mathematical Toolkit. Following exactly the procedure outlined in the mathematical toolkit:
rSun = 100rEarth
2
Surface area = 4 r
The ratio of the Sun's surface are to Earth's surface area is therefore:
2
surface area of Sun = 4 rSun
surface area of Earth 4 r2
Earth
Canceling common factors and substituting yields:
2
surface area of Sun = 100 .
2
surface area of Earth
1
Thus, the surface area of the Sun is 10,000 times larger than the surface area of the Earth.)
a. The Sun's
surface area
is the same
as that of
the Earth.
8
b. The Sun's
surface area is
2
4 100 times
larger than that
of the Earth.
c. The Sun's
surface area
is 100 times
larger than
that of the
Earth.
d. The Sun's
surface area is
2
100 times
larger than that
of the Earth.
e. The Sun's
surface area
is 10,000
times larger
than that of
the Earth.
The speed with which an electromagnetic disturbance (i.e., an electromagnetic wave) moves through space has been found to be
equal to what?
(Solution: Consult text, Chapter 2. Electromagnetic waves travel through the vacuum of space at 300,000 km/s, which is
precisely equal to the experimentally determined value for the speed of light.)
a. The experimentally
determined speed
of light.
9
b. One hundred
times the
speed of
sound in air.
c. The orbital
speed of the
Moon around
the Earth.
d. One-half
the speed
of light.
e. The orbital
speed of
Earth around
the Sun.
Water waves are striking a shoreline with a frequency of 3 waves per second. If the waves have a wavelength of 2 meters per
wave, then the speed of the waves is
(Solution: Consult text Chapter 2. As discussed in class, waves are characterized by 3 fundamental properties: velocity (v),
frequency (f), and wavelength ( ), which are related by the equation:
v= f.
So, if you are given any two of the terms, you can solve for the third one. In this case, you are told that f=3 waves/second and =2 meters/wave. Thus, plugging these into the above formula yields:
v = 2 meters 3 waves ,
wave
second
or
v = 6 meters .
second
Thus, the speed of the waves is 6 meters per second.)
a. 1.5 meters per
second.
b. 5 meters per
second.
c. 2/3 meters per
second.
d. 2 meters per
second.
e. 6 meters per
second.
10 You are generating waves in a shallow pan of water by gently tapping your finger on the water's surface once per second. If you
increase the rate at which you tap the water's surface to two times per second, which of the following will happen?
(Solution: Consult Text Chapter 2. For a given medium (water in this case), increasing the frequency of waves will decrease their
wavelength (this relationship can be seen explicitely by considering the equation v = f , for the case where v remains constant).
In this question, we are increasing the frequency from 1 Hz to 2 Hz. Thus, the wavelength of the resulting waves will be
smaller than it was before. (It will actually be cut in half, although the question does not ask for that specific an answer.) A key
component of this question is to recognize that the speed of the waves is unchanged by the change in frequency.)
a. The wavelength of the
resulting waves will be
smaller than it was before.
c. The speed with which the waves
propagate in the water will be
greater than it was before.
b. The frequency of the
resulting waves will be lower
than it was before.
d. Both (a) and (c) will happen.
e. None of the above; the wavelength,
frequency, and velocity of the
waves will remain unchanged.
11 The light that allows you to see this very interesting reading quiz is made up of waves. In these waves, the distance between
successive peaks (also called "crests") is called the:
(Solution: Consult text Chapter 2. This one is a straight definition: wavelength is defined to be the distance between any two
identical points on two successive waves. Thus, the distance between successive crests is called the wavelength.)
a. Wavelength.
c. Velocity.
b. Frequency.
d. Amplitude.
e. None of the above -- in these waves, the distance between crests is
zero.
12 What is the approximate wavelength of red light in the visible part of the electromagnetic spectrum?
(Solution: Consult text, Chapter 2. This one is a straight fact from the reading: red light is stated in the text to have a
wavelength of about 700 nanometers.)
a. 1 nanometer.
b. 700
nanometers.
c. 1000
Angstroms.
d. 450
nanometers.
e. 700
meters.
13 As stated in your text, the "red line" in the emission spectrum of hydrogen gas has a "rest" wavelength of 6563 Angstroms (656.3
nanometers). Suppose that we observe this line in the spectrum of a star that is rapidly moving towards us. Of the following,
which observed wavelength of this line in a star's spectrum would indicate that the star is approaching us (i.e., moving towards
us) at the greatest speed?
(Solution: Consult text Chapter 2. Since this star is coming towards us, it means that its spectrum will appear to be blueshifted to
us. That means that absorption lines will appear in the spectrum of the star at bluer, or shorter, wavelengths than they would if
the star were at rest. The faster a star is approaching us, the greater its blueshift will be, and the lower the observed wavelengths
of its spectral lines will appear. Thus, for this question, we want the answer that represents the smallest wavelength. Of the
choices given, the shortest wavelength is 6530 Angstroms. Thus, that is the correct answer!)
a. 6530
Angstroms.
b. 6540
Angstroms.
c. 6563
Angstroms.
d. 6570
Angstroms.
e. 6600
Angstroms.
14 The bright star Altair is located at a distance of about 5 parsecs from Earth. What parallax would you expect to be observed for
this star?
(Solution: Consult text Chapter 2. This is a math problem. We know that parallax is related to distance through the formula:
D = 1 , where D is the distance to a star in parsec and p is the measured parallax of the star, in arcsec. So, here we know
p
that D = 5 parsec , thus we have, solving for p :
p= 1 ,
5
or p = 0.2 arcsec .)
a. 0.2 arcsec.
b. 0.2 seconds.
15
YOUR QUESTION
c. 0.2 degrees.
d. 5 arcsec.
e. 60 arcsec.
OK, we come to the last quiz question, and for this, I ask: Based on your reading of the assigned chapter, what is the single
question that you would most like to know the answer to? Note that there's no "right" answer to this, of course -- just ask yourself:
Is there something that confused me while reading the text that I'd like clarification of? Is there something not included in the text
that I would like to know more about? Then, simply write that question down here (it can be as long as you like, it doesn't have to
all fit within the box) -- and so long as you write something, you will get full credit for this question!
Enter question here:
__________________________________________________
ANSWER KEY
Reading Quiz 2: Solutions
angular*
spectrum*
proper*
nebula*
doppler*shift*
elliptical*
telescope
planet*
orion*
galileo*
1. light*year*
nano*meter*
2. d
3. d
4. c
5. b
6. d
7. e
10. a
11. a
12. b
13. a
14. a
15. *
speed*of*light*
electro*
magnetic*
astronomical*
unit*
parallax*
infrared*
frequency*
spectroscopy*
wavelength*
9. e
ANSWER KEY - Page 1
8. a