Physical Science 1 Name: _______________________________________
Exam Three
MULTIPLE CHOICE. Choose the one alternative that best completes the statement or
answers the question. Each question is worth five (5) points.
1) Wave interference occurs for
A) water waves.
B) light waves.
C) sound waves.
D) all of these
E) none of these
Wave interference occurs for ALL waves regardless of type. The answer is D.
2) A floating leaf oscillates up and down two complete cycles in 1 s as a water wave passes
by. The wave's wavelength is 10 m. What is the wave's speed?
A) 10 m/s
B) 40 m/s
C) 2 m/s
D) 20 m/s
E) more than 40 m/s
The frequency is 2 Hz. The wavelength is 10. The product gives the speed. The answer is
D.
3) You dip your finger repeatedly into water and make waves. If you dip your finger more
frequently, the wavelength of the waves
A) stays the same.
B) lengthens.
C) shortens.
The speed of the wave in water is constant, so if you increase the frequency, you decrease
the wavelength since speed = frequency x wavelength. The answer is C.
4) If an electron vibrates up and down 1000 times each second, it generates an
electromagnetic wave having a
A) period of 1000 s.
B) wavelength of 1000 km.
C) frequency of 1000 Hz.
D) speed of 1000 m/s.
E) wavelength of 1000 m.
The wave frequency is the same as electron’s frequency. The answer is C.
April 14, 2009 Page 1
Physical Science 1 Name: _______________________________________
Exam Three
5) Which will warm up quicker in sunlight?
A) a piece of clear glass
B) a piece of colored glass
C) both the same
Clear glass transmits all the light, while colored glass is absorbing some frequencies. If it
absorbs energy it will get warmer. The answer is B.
6) The worst thing you can do for the health of a green-leafed plant is to illuminate it with
only
A) green light.
B) blue light.
B) red light.
C) All are equally naughty.
D) none of these
If you shine green light on the plant, it is all reflected. That is why the plant is green. If it
reflects all the light, it will get no energy and will die. The answer is A.
7) The shortest plane mirror in which you can see your entire image is
A) equal to your height.
B) about 3/4 your height.
C) half your height.
B) about 1/3 your height.
C) dependent on your distance from the mirror.
We worked this problem for a take-home. The answer is C.
8) Light refracts when traveling from air into glass because light
A) intensity is greater in air than in glass.
B) frequency is greater in glass than in air.
C) intensity is greater in glass than in air.
D) frequency is greater in air than in glass.
E) travels slower in glass than in air.
Refraction is due to differing speeds of light in two different media. The answer is E.
9) A primary rainbow is brighter than a secondary rainbow because
A) there is one less reflection inside the water drops.
B) the secondary bow is a dim reflection of the primary rainbow.
C) sunlight reaching it is more intense.
D) larger drops produce primary rainbows.
E) none of these
Look at the pictures in the text. Secondary rainbows involve two reflections inside the
raindrop. The answer is A.
April 14, 2009 Page 2
Physical Science 1 Name: _______________________________________
Exam Three
10) When a clean surface of potassium metal is exposed to blue light, electrons are emitted.
If the intensity of the blue light is increased, which of the following will also increase?
A) the threshold frequency of the ejected electrons
B) the time lag between the absorption of blue light and the start of emission of the
electrons
C) the maximum kinetic energy of the ejected electrons
D) the number of electrons ejected per second
E) none of these
This is the photoelectric effect. The intensity of light relates to how many photons per
second hit the surface of the metal. This number determines how many electrons will be
ejected from the metal. The answer is D.
Problems: Show all your work to receive as much partial credit as possible.
Constants: Speed of electronmagnetic waves = 3 x 108 meters/second.
Speed of sound in air = 330 meters/second.
Speed of sound in water = 1500 meters/second
Acceleration due to gravity, g = 10 meters/second2
Planck’s Constant, h= 6.6 x 10-34 Joule-sec
11) Ultrasound is used in medical applications to do non-invasive imaging of body organs.
The benefit is that ultrasound doesn’t damage tissues like x-rays do. If the frequency of
the ultrasound is 2 x 107 Hz, what is the wavelength of these sound waves in the body?
(Hint: The human body is mostly water and therefore transmits sound in the same way
that water does.)
wavelength speed / frequency
7
wavelength 1500 /2 10
wavelength 7.5 10 5
12) The sun is about 150 million kilometers from the earth. How long does it take light to
travel from the sun to the earth?
Distance = velocity x time, so time = distance/velocity
Distance = 150 million km = 150 x 106 x 103 meters
Time = 150 x 109/3 x 108 = 500 seconds or a little over 8 minutes
April 14, 2009 Page 3
Physical Science 1 Name: _______________________________________
Exam Three
13) The standard red-light laser used for classroom pointers, shop tools, etc. has a wavelength
of about 633 nanometers. (1 nanometer = 10-9 meter) What is the frequency of this
light?
Frequency = speed/wavelength = 3 x 108/633 x 10-9
Frequency = 4.74 x 1014
14) What is the energy of a photon of ultraviolet light with a wavelength of 3 x 10-7 meters?
E hf
8
310
c
f 7
11015
310
34 15
E 6.6 10 110
E 6.6 1019
April 14, 2009 Page 4