Physics 7120                Name ______________________
Midterm Exam

1. Sound in air is composed of
a. longitudinal waves
b. transverse waves
c. either transverse or longitudinal waves
d. neither transverse nor longitudinal waves
e. transverse waves on Mon, Wed, and Fri but otherwise longitudinal.

2. Lying on a dock on Lake Lanier after finishing the 7120 course, a student noted that waves reached the dock every 5 seconds and that the distance between crests was about 3 meters. Quick as a flash she calculated the wave speed to be
a. 5/3 m/sec
b. 15 m/sec
c. 3/5 m/sec
d. can't be determined from the data given.

3. When a real image of an object is formed on a screen by a lens, the image must be
a. inverted
b. larger than the object
c. smaller than the object
d. none of the above is necessarily true.

4. In a rainbow, light is
a. refracted
b. reflected
c. both refracted and reflected

5. A sunset appears red because
a. blue light is scattered out of the sun's rays as they pass through a longer-than-normal air 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.

6. When a source of sound approaches, measurements will show an increase in the sound's
a. speed
b. frequency
c. wavelength
d. all of these
e. none of these

7. In AM radio transmission,
a. a high frequency sound is transmitted.
b. sound is transmitted on a radio carrier wave.
c. the sound is amplitude modulated by the electromagnetic carrier wave.
d. an "electric image" of the sound varies the amplitude of a carrier electromagnetic wave.

8. Which way will the light ray bend from its original path when entering the glass below?
9. An underlying reason for the warmth of greenhouses is that
a. whitewash on the outer surface of the glass filters ultraviolet light.
b. glass is transparent to incoming high frequency energy but opaque to low frequency re-radiated energy.
c. re-radiated energy from plants travels at too low a speed to get through the glass and is trapped inside.
d. some of the sunlight incident upon plants is converted into energy by photosynthesis

10. An oar partially immersed in water appears "broken" because of
a. refraction
b. interference
c. diffraction
d. absorption
e. polarization

11. Which of the following is a property of a light wave but not of a sound wave
a. frequency
b. wavelength
c. polarization
d. interference
e. Doppler effect

12. The characteristic quality of a sustained musical instrument sound is determined mainly by
a. its pitch
b. its amplitude
c. the relative amplitudes of the upper harmonics of the tone
d. the attack and decay transients and vibrato in the tone

13. Light is emitted when
a. electrons jump from lower to higher levels
b. molecules vibrate
c. electrons jump from higher to lower levels
d. electrons are ejected from atoms

14. Of the following types of electromagnetic radiation, the one with the shortest wavelength is
a. microwaves
b. radio waves
c. visible light
d. ultraviolet

15. The type of wave most likely to diffract around a building would be
a. an AM radio carrier wave
b. a microwave
c. visible light
d. x-rays

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

17. Which of the following cannot produce ionization and the radiation damage effects associated with ionizing radiation
a. x-rays
b. gamma rays
c. microwaves
d. ultraviolet

18. A vibrating string will have certain natural vibration frequencies or resonances because
a. it is always driven at those frequencies
b. all objects vibrate in harmonics
c. all other frequencies tend to be destroyed by destructive interference.
d. these frequencies are enhanced by constructive interference

19. If you want to achieve higher resolution with an electron microscope, you use
a. higher speed electrons because their wavelengths are shorter
b. higher speed electrons because their wavelengths are longer
c. lower speed electrons because their wavelengths are shorter
d. lower speed electrons because their wavelengths are longer

20. When a vibrating metal rod causes the air in a tube to vibrate, the waves in the air have
a. the same speed as those in the rod
b. the same frequency as those in the rod
c. the same wavelength as those in the rod
c. the same amplitude as those in the rod

21. The velocity of photoelectrons emitted from a surface by the photoelectric effect is determined by
a. the total energy of the light
b. the intensity of the light
c. the frequency of the light
d. the velocity of the light

22. The wave property that limits the fineness of detail which you can see with a light microscope is diffraction, which smears out the image. To get the finest detail you should
a. use longer wavelength light
b. use brighter light
c. use a lens with greater magnification
d. use shorter wavelength light

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

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

25. The phenomenon of beats is a result of
a. interference
b. reflection
c. diffraction
d. refraction

26. Light is refracted when it passes from air into the glass of a lens because
a. it strikes the lens at an angle
b. its speed in the glass is slower than in air.
c. it is partially absorbed by the glass
d. its amplitude changes at the glass interface.

27. Explain with the help of a sketch why atoms emit only certain colors of light. Explain why they absorb the same colors strongly.

28. Of the following radiation types, which has the highest frequency?
a. gamma rays
b. radio waves
c. ultraviolet
d. blue visible light

29. When an electron makes a transition from a high energy state to a lower energy state
a. it emits a photon of energy equal to the energy of the higher state
b. it absorbs a photon
c. it emits a photon of energy equal to the difference in energy between the higher and lower states.
d. nonsense - the electron is forbidden to make such a transition.

30. Which colors of light could you mix in equal proportion an get yellow light as a resulting color. Is this the only way to get that yellow ? Explain. What color would you mix in equal proportions with yellow to get white light as a result?

31. Why is the sky blue?

32. A vibrating string of length 120 cm vibrates in a standing wave mode with three distinct loops in the vibration pattern when driven by a 120 Hz vibrator. The wave velocity in the string is
a. 1 m/sec
b. 3 m/sec
c. 150 m/sec
d. 96 m/sec
e. none of the above

33. The temperature of a distant incandescent hot object can be determined by measuring
a. the total radiation received from it.
b. the wavelength at which the emission spectrum peaks
c. the shortest wavelength emitted
d. the shape of the curve of emission as a function of frequency.

34. The resolution of the wave-particle paradox for light is
a. light exhibits its wave properties in some experiments and particle properties in others - having an essential dual nature.
b. light always behaves as a wave but other rays can show both wave and particle properties.
c. no one knows what light is
d. light only appears to have particle properties; it is essentially a wave phenomenon.

35. On some days, air nearest the ground is colder than the air that is higher up. On one of these days, sound waves
a. tend to be refracted upward
b. tend to be refracted downward
c. travel without refraction through the air.

36. The different spectral colors of light correspond to different
a. frequencies
b. intensities
c. polarities
d. velocities

37. Light intensity from an incandescent source is plotted as a function of frequency as shown in the radiation curve. If this light is first passed through a cool gas, the resulting radiation curve would look like
This best illustrates that the atoms of gas have
a. been excited to higher energy levels
b. absorbed part of the light
c. amplified selective resonant frequencies of the transmitted light.

38. Which color light has the most energy per photon?
a. red
b. green
c. blue
d. all the same

39. To accommodate for viewing close objects, the eye must change its
a. focal length
b. image distance
c. aperture
d. f-number
whereas to focus closely the camera must change its
a. focal length
b. image distance
c. aperture
d. f-number

40. The quantum of light is called a
a. quark
b. lighton
c. lepton
d. photon
and its energy
a. increases with light frequency increases
b. increases with wavelength increases
d. increases with frequency decrease.
d. is independent of wavelength.

41. 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
a. the lens is too strong
b. the lens is too weak
c. of astigmatism
d. the focal length is too short

42. Assuming the settings to be the same, oscilloscope display A represents a wave of higher
whereas display B represents a wave of higher
a. amplitude
b. frequency
c. velocity
d. wavelength

43. When a 1000 Hz tuning fork is struck and held over the open end of a cylindrical tube filled with water, the first resonance occurs when the water level is lowered to 8.5 cm below the top of the tube. This length corresponds to
a. one quarter wavelength for the sound wave
b. one half wavelength for the sound wave
a. one  wavelength for the sound wave
a. nonsense ... it is related to the frequency and not to the wavelength.

The velocity of sound corresponding to this resonant frequency is
a. 340 m/s
b. 680 m/s
c. 170 m/s
d. 85 m/s

44. The photoelectric effect uses light to
a. eject electrons from metals
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 particle or waves..
d. the reflective property of metals

45. A spectrum of colors seen in gasoline on a wet street is primarily a result of
a. interference
b. polarization
c. refraction
d. scattering
e. diffraction

a. the light reaching the eye is polarized by double reflection
b. only the higher frequencies of light resonate with the gasoline and H2O molecules.
c. the thin film of gasoline spreads the light out into its component colors.
d. some colors of light reflecting from the gasoline surface are canceled by light reflecting from the water surface

46. You are swinging a child on a playground swing and reflect on the nature of this simple pendulum. You judge that if a second child climbed onto the swing with the first,  the pendulum period will
a. increase
b. decrease
c. stay the same
d. the mass has increased, slowing the pendulum
e. the period is independent of the mass
f. pendulum periods increase with mass

47. Pitch of sound corresponds to
a. frequency
b. noise
c. loudness
d. intensity
whereas amplitude of sound waves corresponds to
a. frequency
b. noise
c. loudness

48. Compared to a soft sound, the speed of a loud sound is
a. less
b. greater
c. the same

and compared to a low-frequency sound,  higher-frequency sound travels
a. slower
b. faster
c. the same

49. When you blow over the top of a coke bottle, you produce the cavity resonance frequency of the bottle. If you add water and then  blow over  it,
a. The pitch would be higher and the period would be longer
b. The pitch would be higher and the period would be shorter
c. The pitch would be lower  and the period would be longer
d. The pitch would be lower and the period would be shorter