Physics 712    Name ________________________
Midterm Exam

1. Smoke sometimes appears blue because
a. some types of smoke particles are blue
b. very fine smoke particles selectively scatter the short wavelengths to your eyes
c. smoke absorbs other colors
d. blue light is more easily transmitted by smoke

2. An open gas tap is heard before the gas can be smelled. The best statement of the reason is
a. the speed of sound is greater than the speed of smell
b. sound is a longitudional wave while smell is a transverse wave.
c. sound transfers energy from molecule to molecule while smell requires that the original molecules reach your nose.
d. smell travels by random molecular motion while sound does not require molecules to transmit it.

3. Wave crests reach your boat every 4 seconds. The distance between crests is 6 meters. The frequency of the wave motion is
a. 0.25 Hz
b. 1.5 Hz
c. 24 Hz
d. 0.67 Hz

and the wave speed is
e. 1.5 m/s
f. 24 m/s
g. 9 m/s
h. 144 m/s

4. Sound in air is a
a. longitudional wave
b. transverse wave
c. can't be determined to be either longitudional or transverse.

5. Name two similarities and two differences in the properties of sound and light.

6. A sandbag pendulum is positioned over a moving belt, and a hole is poked in the bag so that the sand pouring out will trace out a sine wave on the moving belt. As the sand empties out, decreasing the mass of the bag, the pendulum period will
a. increase
b. decrease
c. stay the same

7. If the wavelength of a 200 Hz sound is 5.5 feet, then the wavelength of a 2000 Hz sound is
a. 55 ft
b. 0.55 ft
c. 5.5 ft
d. not determinable because the speed is not given
e. shorter, but the number cannot be inferred from the data given.

8. The speed of sound in air would be increased by
a. increasing the pitch of the sound.
b. increasing the loudness of the sound.
c. changing the quality of the sound
d. all of the above
e. none of the above.

9. When a sound source approaches you, your measurements will show an increase in the sound's
a. frequency
b. wavelength
c. speed
d. all of these
e. none of these
and when the sound source recedes from you, the measurements will reveal an increase in the sound's
a. frequency
b. wavelength
c. speed
d. all of these
e. none of these

10. The phenomenon of beats is a result of sound wave
a. refraction
b. reflection
c. interference
d. diffraction

11. "Standing waves" on a string are most closely associated with
a. diffraction
b. resonance
c. longitudional vibrations
d. destructive interference

12. A tube is filled with water and then the water is gradually lowered while sounding a 1000 Hz tuning fork above the tube. The sound becomes louder when the distance to the water surface is 8.5 cm, showing that the air column resonant frequency is the same as the tuning fork frequency. Neglecting end corrections, this tells you that the sound wavelength is about
a. 8.5 cm
b. 17 cm
c. 25.5 cm
d. 34 cm

13. Which of the following is most closely associated with wave behavior and most difficult to explain with a beam of particles
a. reflection
b. polarization
c. refraction
d. photoelectric effect

14. If you wished to increase th resolution of an imaging process in order to view smaller objects, you could
a. use lower frequency waves
b. increase the intensity of the waves used
c. decrease the wavelength of the waves used
d. decrease both frequency and wavelength of the waves used.

15. To produce a rainbow, light is
a. refracted
b. reflected
c. both refracted and reflected
d. neither refracted nor reflected

16. The velocity of a sound wave depends upon the
a. frequency of the wave
b. amplitude
c. pitch of the sound
d. medium through which it travels
17. The kind of radiation most often associated with "radiant heat" felt from a hot object is
a. heat waves
b. microwaves
d. visible light

18. In any imaging process, the size of the smallest object which can be resolved under ideal conditions is about equal to the wavelength of the radiation used for the imaging. If the speed of sound in tissue is about 1500 m/s and the frequency of sound used in an ultrasonic imager for medical purposes is 1 MHz = 1,000,000 Hz, the smallest sized object which can be resolved with this imager is about
a. 0.015 m
b. 6.6 m
c. 0.0015 m
d. 0.15 m

19. The speed of sound in air is 340 m/s. The wavelength in air of a sound wave of frequency 170 Hz is
a. 2 m
b. 0.5 m
c. 4 m
d. 510 m

20. Light rays coming from a fish under water and entering the air at an angle other than 90°
a. will be bent downward toward the water surface
b. will be bent upward toward the vertical
c. will not be bent
d. may be bend upward or downward, depending upon the color of the light

21. A sunset appears red because
a. blue light is scattered out of the sun's rays as they pass through the longer-than-normal light path
b. air tends to absorb blue light more than red light
c. scattering in air progressively lowers the frequency of the light in its long air path
d. blue light is refracted out of the beam in the long air path.

22. Of the two sketches of oscilloscope displays, the one on the left represents a signal of

23. Show the directions of the paths of travel of the toy cart as it rolls across the pieces of carpet where its speed is slower. Be sure you have clearly depicted any changes in direction.

24. The kind of signal that you would most likely be able to receive on your antenna if you lived on the opposite side of a mountain from the transmitting antenna would be
c. TV picture
d. Microwave telephone transmission

because
e.  the TV signal is transmitting light
f. it has the longest wavelength and would therefore diffract around the mountain.
g. it has the highest frequency and would therefore diffract around the mountain
h. FM signals can be detected better because interference of waves removes the amplitude modulation of waves.

25. The speed of sound in air would be increased by
a. increasing the pitch of the sound.
b. increasing the loudness of the sound.
c. changing the quality of the sound
d. all of the above
e. none of the above.

26. When a sound source approaches you, your measurements will show an increase in the sound's
a. frequency
b. wavelength
c. speed
d. all of these
e. none of these
and when the sound source recedes from you, the measurements will reveal an increase in the sound's
a. frequency
b. wavelength
c. speed
d. all of these
e. none of these

27. The phenomenon of beats is a result of sound wave
a. refraction
b. reflection
c. interference
d. diffraction

28. "Standing waves" on a string are most closely associated with
a. diffraction
b. resonance
c. longitudional vibrations
d. destructive interference

29. The property of light which makes possible the formation of clear images by the eye is
a. reflection
b. refraction
c. diffraction
d. interference

30.  The spreading out of waves past a small opening is a result of
a. reflection
b. refraction
c. diffraction
d. interference

31. If a larger mass were suspended on a hanging spring, the natural frequency of its vibration would be
a. higher
b. lower
c. the same

whereas if a larger mass were placed on a pendulum without changing anything else about the pendulum, its natural frequency would be
d. higher
e. lower
f. the same.

32. The colors seen in a thin oil film on water are primarily the result of light
a. interference
b. refraction
c. diffraction
d. reflection
e. polarization

where
a. the light reaching the eye is polarized by double reflection
b. only the higher frequencies of light resonate with the oil and water molecules
c. the thin film of oil spreads the light out into its component colors
d. light reflecting from the oil surface is partially canceled by light reflecting from the water surface below it.

33. A relatively cool star will most likely exhibit the color
a. cool blue
b. yellow
c. white
d. red

34. Which type of photon has the greatest energy?
a. microvave
b. visible light
c. x-ray
d. ultraviolet

35. Which of the following spectra would be characteristic of a hot star surrounded by cool gases?

36. The higher frequency portions of the ultraviolet part of the electromagnetic spectrum are more dangerous than the lower frequency portions because
a. they are invisible, while the lower frequency UV can be seen
b. they can produce ionization
c. they have shorter wavelengths
d. they produce rotations of molecules

37. Laser light through a narrow slit is spread by
a. reflection
b. refraction
c. interference
d. diffraction

and if the slit is made narrower
a. the light beam is spread more
b. the light beam is spread less
c. the light beam is spread the same amount because it's wavelength is much smaller than the slit

38. Light reaching the earth directly from the sun is
a. highly polarized
b. elliptically polarized
c. unpolarized
d. linearly polarized

and light reflected from a wet beach is
a. polarized in the direction of light travel
b. polarized parallel to the surface it reflects from
c. polarized perpendicularly to the surface it reflects from
d. unpolarized; it is interference which causes the glare

39. The photoelectric effect uses light to
a. eject electrons from metal
b. create electron-positron pairs
c. reflect from metal
d. change into electrons

and demonstrates
a. the wave nature of light
b. the particle nature of light
c. that light can be either particles or waves
d. the reflective property of metals

40. A quantum of light is called a
a. quark
b. lighton
c. photon
d. lepton

and its energy
a. increases with light frequency increases
b. increases with wavelength increases
c. increases with frequency decrease
d. is independent of wavelength

41. Visible light is emitted when
a. electrons jump from higher to lower levels
b. molecules vibrate
d. electrons are ejected from atoms.

and the color of the light emitted depends upon
a. the energy of the upper level
b. the difference in energy between the initial and final states
c. the distance between the orbits
d. the speed of ejection of the electrons

42. If a star appears to be red to the eye, the peak of its radiation curve is in the
a. infrared
b. ultraviolet
c. visible
d. can't be determined from the information given

43. The resolution of the wave-particle paradox for light is that
a. light exhibits its wave properties in some experiments and particle properties in others-having an essentially dual nature.
b. light behaves like waves on Mondays, Wednesdays, and Fridays and like particles on other days.
c. no one knows what light is
d. light always behaves as a wave but some other rays can show both wave and particle properties.

44. The color you would get by mixing equal amounts of green and red light would be
a. yellow
b. white
c. blue
d. magenta

45. The color you would get by mixing equal amounts of yellow and blue light would be
a. red
b. white
c. blue
d. magenta

46. The wavelength of a high speed electron is
a. shorter than that of a low speed electron
b. longer than that of visible light
c. longer than that of a low speed electron
d. non existent: electrons are particles!

47. The velocity of photoelectrons emitted from a surface by the photoelectric effect is determined by
a. the voltage of the electrons
b. the frequency of the light
c. the intensity of the light
d. the velocity of the light

48. Explain how the colors of light emitted from atoms can be used to indentify them, even in distant stars. Can the colors which are absorbed be used for the same purpose?

49. The lens of a nearsighted person's eye focuses parallel rays of light
a. on the retina
b. behind the retina
c. in front of the retina
d. does not focus parallel rays at all

because
a. the lens is too strong
b. the lens is too weak
c. of astigmatism
d. the eye's length is too great.

50. To accomodate for viewing close objects, the eye's lens must change its
a. focal length
b. image distance
c. aperture
d. iris opening

whereas to focus closely the camera must change its
a. focal length
b. image distance
c. aperture
d. f-number

51. Blue light differs from red light in that
a. its intensity is greater
b. its frequency is higher
c. its wavelength is longer
d. its quantum energy is lower