## Exam 1 Fall 2000 (text format)

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1.	(20)Fill in the blanks:

a)	____________________  the rate at which an object's velocity changes

b)	____________________  the angular distance between the horizon and an object in the sky

c)	____________________  the imaginary sphere on which objects in the sky appear to reside

d)	____________________  a measure of how much an ellipse deviates from a perfect circle (e=0)

e)	____________________  the Sun's apparent annual path against the constellations of the zodiac

f)	____________________  the weakest of the four fundamental forces

g)	____________________  energy of motion; defined as ½ mv2

h)	____________________  the product of an object's mass and velocity.

i)	____________________  the compact center of an atom made from protons and neutrons

j)	____________________  energy stored for later conversion into kinetic energy

k)	____________________  a measure of the angle formed by extending imaginary lines outward from our eyes to span an object

l)	____________________  a large glowing ball of gas that generates energy through nuclear fusion
in its core.

m)	____________________  the spectrum of radiation produced by an opaque object that depends only on the object's temperature.

n)	____________________  describes an object in freefall

o)	____________________  equal to the speed of the wave divided by the wavelength of the wave

p)	____________________  measured in cycles per second

q)	____________________  measured in distance traveled over a unit of time

r)	____________________  equal to the speed of the wave divided by the wave's frequency

s)	____________________  the distance between two adjacent peaks of the wave

t)	given the frequency of a photon traveling in space, you can determine its:

____________________   and its ____________________   .

2)	-2-According to the universal law of gravitation, if you double the distance between two objects, then the gravitational force between them will  (circle the correct answer)
a)	decrease by a factor of 2.
b)	increase by a factor of 2.
c)	decrease by a factor of 8.
d)	increase by a factor of 4.
e)	decrease by a factor of 4.

3)	-2-According to the universal law of gravitation, if you triple the mass of one attracting object and double the mass of the other, then the gravitational force between them will:
a)	increase by a factor of 1.5.
b)	decrease by a factor of 5.
c)	decrease by a factor of 6.
d)	increase by a factor of 5.
e)	increase by a factor of 6.

4)	-2-The equation, F=ma, describes how much force is required to
a)	change the object's mass.
b)	keep an object moving at zero acceleration.
c)	hold an object in place.
d)	have an equal but opposite reaction.
e)	change an object's velocity over a given time interval.

5)	-2-When a spinning ice skater pulls in his arms, he spins faster because
a)	his body feels less gravitational force.
b)	there is less friction with the ice.
c)	there exists an unbalanced reaction force.
d)	because angular momentum is conserved.
e)	terminal velocity is not reached.

6)	-4-Examine the next figure of a low-mass star orbiting a much higher mass star, and fill in the
blanks with the correct letter:

a)	Increasing speed: ____ to ____

b)	Decreasing speed: ____ to ____

c)	Smaller star has greatest speed ____

d)	Smaller star has lowest speed ______

7)	-3-How is a low-mass star orbiting a much higher mass star in an eccentric orbit like a skater pulling in his arms to rotate faster? Be specific!

8)	-2-The Earth has a mass of about   kg; an average student has a mass of about 75 kg.  The students taking this exam, should know that
a)	they could use the force
b)	the Earth is pulling on them with a force that is much greater than the force they are exerting on the Earth
c)	each of them is exerting an equal and opposite force on the Earth
d)	there is a net force between each of them and the Earth, but the difference is extremely small
e)	they must be exerting a much smaller force on the Earth in order to accelerate.

9)	-2- How are wavelength, frequency, and energy related for photons of light?
a)	Longer wavelength means higher frequency and lower energy.
b)	Longer wavelength means lower frequency and higher energy.
c)	Longer wavelength means higher frequency and higher energy.
d)	Longer wavelength means lower frequency and lower energy.
e)	Because different photons travel at different speeds, there is no simple relationship.

10)	-2- From shortest to longest wavelength, which of the following correctly orders the different categories of electromagnetic radiation?
a)	gamma rays, X rays, ultraviolet, visible light, infrared, radio
b)	infrared, visible light, ultraviolet, X rays, gamma rays, radio
c)	visible light, infrared, X rays, ultraviolet, gamma rays, radio
d)	gamma rays, X rays, visible light, ultraviolet, infrared, radio
e)	radio, infrared, visible light, ultraviolet, X rays, gamma rays

11)	-2- From highest energy to lowest energy, which of the following correctly orders the different categories of electromagnetic radiation?
a)	gamma rays, X rays, ultraviolet, visible light, infrared, radio
b)	visible light, infrared, X rays, ultraviolet, gamma rays, radio
c)	X rays, gamma rays, visible light, ultraviolet, infrared, radio
d)	visible light, gamma rays, X rays, ultraviolet, infrared, radio
e)	radio, infrared, visible light, ultraviolet, X rays, gamma rays

12)	-5-Following is a schematic of the first five energy levels of the hydrogen atom.  Assume the electrons are absorbing energy and thus producing an absorption spectrum.

a)	How many possible transitions are there? _____________

b)	Which transition represents the smallest energy change?  From ________ to _________

c)	Which transition represents the largest energy change?  From ________ to _________

d)	Which transition represents the shortest wavelength? From ________ to _________

e)	Which transition represents the longest wavelength? From ________ to _________

13)	-4- How can the hydrogen atom, that has only one electron, generate lines occurring at more than one wavelength (multiple lines)?

14)	-5- Suppose the surface temperature of the Sun were about 36,000 K, rather than 6,000 K.  List
two ways in which the thermal radiation spectrum of the Sun would be different.

15)	-2- A planet is five astronomical units from the Sun.  What is the ratio of the distance of this
planet from the Sun to the distance of the Earth from the Sun?

16)	-2- Use Newton's version of Kepler's third law: suppose a solar system has a star that is 9 times as massive as our Sun. If that solar system has a planet the same size as Earth orbiting at the same distance as the Earth from our Sun, what is the approximate orbital period of the planet?
a)	1 year
b)	3 years
c)	1/9 of a year
d)	9 years
e)	1/3 of a year

17)	-2- The spectrum of neon gas looks like
a)	argon, which is also an inert gas
b)	krypton, since it has similar chemical properties
c)	ionized sodium
d)	no other element
e)	none of the above

18)	-2- When an electron goes from a higher energy state to a lower energy state, the atom
a)	can absorb a photon of any frequency.
b)	emits a photon of a specific frequency.
c)	absorbs a photon of a specific frequency.
d)	can emit a photon of any frequency.
e)	absorbs several photons of a specific frequency.

19)	-2- When an atom absorbs a photon containing energy, the electron
a)	moves from a lower energy level to an upper one.
b)	transition causes the atom to become de-excited.
c)	moves from an upper energy level to a lower one.
d)	always escapes from the atom (the atom is ionized).
e)	causes an isotope of the atom to form.

20)	-2- An electron in an atom loses energy going from a higher to a lower energy level by
a)	absorbing a photon equal in energy to its own energy drop.
b)	losing kinetic energy.
c)	losing gravitational potential energy.
d)	releasing a photon equal in energy to its own energy drop.
e)	exchanging gravitational potential energy for kinetic energy.

21)	-6-> Here is an actual image of the hourglass nebula (also, see overhead projection).   Which part must you observe to see:

a)	a continuous spectrum? _____________________________________

b)	an emission spectrum?  _____________________________________

c)	Part of the cloud of gas lies between us and another hot thermal source.  What kind of spectrum is seen when looking at this location?

22)	-2- You have inherited four high-quality telescope eyepieces from your grandmother: 60 mm, 40 mm, 30 mm, and 10 mm in focal length.  You purchase a telescope so that you can put them to good use.  Which of the following combinations of focal length of the telescope (objective lens) and eyepiece will give you the greatest magnification?
a)	1200 mm and 40 mm
b)	1200 mm and 30 mm
c)	1200 mm and 60 mm
d)	1200 mm and 10 mm

23)	-2- What makes the North Star, Polaris, special?
a)	It is the star at the zenith anywhere in the northern hemisphere.
b)	It is the star directly on the northern horizon.
c)	It appears very near the north celestial pole.
d)	It can be used to determine your longitude on Earth.
e)	It is the brightest star in the sky.

24)	-4-The light-collecting area of a telescope is described using the area of a circle: A=3.14 r2.  How many more times light-collecting area does the 10-m diameter Keck telescope atop Mauna Kea in Hawaii have compared to the approximately 2-m diameter mirror in the orbiting Hubble Space Telescope?  Show all logic here (you shouldn't need a calculator).

25)	-2- At which point does a particular Earth-crossing asteroid have the greatest kinetic energy?
a)	approaching the Earth at 1 km/hr, 400,000 km away
b)	orbiting 400 km above the Earth at 27,000 km/hr
c)	just about to strike the surface of the Earth at 40,000 km/hr
d)	an instant after it hits the Earth's surface

26)	-2- The gravitational potential energy of this asteroid is
a)	greatest when it is its maximum distance from Earth
b)	greatest when it is orbiting the Earth
c)	greatest as it smashes into the ground.
d)	the same at all positions

27)	-3- You spy an asteroid and its tiny moon (Ida and Dactyl shown here) heading straight for Earth. Ida is 50 times more massive than Dactyl.  Will you have to use more force or less force to divert it from the Earth?  Explain, using the word "inertia" (correctly) in your explanation.

28)	-4- As they cool, the temperatures of white dwarfs (the dying remnant of a Sun-like star) drop
from about 100,000 Kelvin to (eventually) absolute zero.  In general, describe two changes in the
thermal radiation spectrum of white dwarfs as they cool.

29)	-2- Why is it a good idea in any experiment to take many measurements and average the results?
30)	 -4- Take a look at the spectra being projected on the screen.  What is the evidence for the
existence of iron in the atmosphere of the Sun?

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