Excursions in Physics

Third Hour Exam

Oscillators, Waves, Sound

March 31, 1998

For every question, also consider as a possible answer

E) none of the above

Possibly useful information:

v = x / t p = m v T = 2

a = v / t PE = m g h T = 2

v = v_i + a t PE = (¹/₂) k x² v =

x = x_i + v_i t + (¹/₂) a t² KE = (¹/₂) m v² v=(wavelength) x (frequency)

v = r F = k x L = (n) x (half wavelength)

F = m a E_i = E_f

F₁₂ = - F₂₁ p_i = p_f

w = mg F = p / t

g = 9.8 m/s² 10 m/s²

For every question, also consider as a possible answer

E) none of the above

E) none of the above

1. Increasing the amplitude of a mass-and-spring simple harmonic oscillator makes its period

A) longer

B) shorter

C) unchanged;

As with all simple harmonic oscillators, the period is independent of the amplitude

2. Increasing the mass m of a mass-and-spring simple harmonic oscillator makes its period

A) longer ; T = 2

B) shorter

C) unchanged

3. Increasing the spring constant k of a mass-and-spring simple harmonic oscillator makes its period

A) longer

B) shorter ; T = 2 ; increasing k decreases T

C) unchanged

4. A mass-and-spring simple harmonic oscillator has maximum kinetic energy

A) at its equilibrium position

At its equilibrium position the potential energy is zero, PE = (1/2) k x²

so the kinetic energy is at its maximum

B) when its displacement equals its amplitude

PE = max for x = Amplitude

C) half way between equilibrium and amplitude

D) two-thirds of the way between equilibrium and amplitude

5. A mass-and spring simple harmonic oscillator has maximum potential energy at

A) at its equilibrium position

PE = 0 for x = 0

B) when its displacement equals its amplitude

PE = max for x = Amplitude

C) half way between equilibrium and amplitude

D) two-thirds of the way between equilibrium and amplitude

6. The amplitude of a simple harmonic oscillator is

A) the time required for one oscillation

B) the number of oscillators per second

C) the energy stored in the oscillations

D) the maximum distance moved from equilibrium

7. The period of a simple pendulum depends upon its

A) mass

B) amplitude

C) length; T = 2

D) all of the above

The period depends only upon the length and the acceleration of gravity.

The period of any simple harmonic oscillator is independent of the amplitude.

The period of a pendulum is independent of the mass.

8. The period of a certain simple harmonic oscillator is 0.01 s; its frequency is

A) 0.1 Hz

B) 1.0 Hz

C) 10.0 Hz

D) 100.0 Hz; f = 1/T = 1/0.01 s = 100 /s = 100 Hz

9. The frequency of a certain oscillator is 50 Hz; it's period is

A) 0.2 s

B) 0.02 s ; T = 1 / f = 1 / 50 Hz = 0.02 s

C) 0.002 s

D) 0.0002 s

10. If you apply a force to an oscillator at its natural frequency, you will produce motion

A) at exactly twice that frequency

B) at exactly one-half that frequency

C) with large amplitude

This is the whole idea of resonance.

D) with an amplitude that dies out or gets smaller.

11. There are "signals" of many different frequencies coming into the antenna of your radio. Only the one with a particular frequency is amplified and produces the sound you listen to. This is an example of

A) damping

B) amplitude degeneration

C) timbre or quality

D) resonance

12. Where is the speed of a simple harmonic oscillator zero?

A) at its equilibrium position

B) when its displacement equals its amplitude

Here, at max displacement, the PE is max and KE is zero

KE = 0 requires v = 0

C) half way between equilibrium and amplitude

D) two-thirds of the way between equilibrium and amplitude

13. Like a transverse wave, a longitudinal wave has a/an

A) amplitude

B) wavelength

C) period

D) all of the above

14. Which of the following is a longitudinal wave?

A) light

B) wave on a string

C) sound

D) all of the above

 

15. The individual vibrations or disturbances of a longitudinal wave move

A) in the same direction as the wave itself

B) perpendicular to the wave itself

16. A wave has a frequency of 20 Hz and travels 5 m in one second. It has

A) a wave speed of 100 m/s and a wavelength of 4 m.

B) a wave speed of 100 m/s and a wavelength of 1/4 m.

C) a wave speed of 5 m/s and a wavelength of 1/4 m

v is given; the wave "travels 5 m in one second."

v = 5 m/s

v = (frequency) x (wavelength)

5 m/s = 20 (1/s) x [wavelength]

5 m/s = 20 (1/s) x [ (1/4) m]

wavelength = (1/4) m

D) a wave speed of 5 m and a wavelength of 4 m

17. For standing waves, nodes are

A) always a wavelength apart; nodes are always half a wavelength apart

B) regions of greatest amplitude;

nodes are regions of smallest amplitude -- zero

antinodes are regions of greatest amplitude

C) regions of greatest frequency

everything on a standing wave has the same frequency

D) always two wavelengths apart ; nodes are always half a wavelength apart

E) none of the above

18. For standing waves, antinodes

A) are a wavelength apart ; antinodes are always half a wavelength apart

B) have the greatest frequency

everything on a standing wave has the same frequency

C) alternate with nodes

D) all of the above

19. For standing waves on a string,

A) a node is located at each end

B) a whole number times half the wavelength equals the length of the string

C) the whole "pattern" of standing waves occurs only for certain frequencies

D) all of the above

20. On a string that is 2.0 m long, standing waves may be formed with the following wavelengths:

(Yes, the fundamental frequency will have a wavelength of 4.0 m).

A) 4.0 m, 2.0 m, 0.5 m

B) 4.0 m, 2.0 m, 1.5 m

C) 4.0 m, 1.5 m, 0.75 m

D) 4.0 m, 1.67 m, 0.67 m

L = n x (half a wavelength)

n = any integer

half a wavelength = L / n

wavelength = 2 L / n

L = 2.0 m

wavelength = 2 x 2.0 m / n = 4.0 m / n

wavelength = 4 m, (4/2) m, (4/3) m, (4/4) m, (4/5) m,

(4/6) m, (4/7) m, (4.8) m, etc

wavelength = 4.0 m, 2.0 m, 1.33 m, 1.00 m, 0.80 m,

0.67 m, 0.57 m, 0.50 m, etc

21. Standing waves can occur when

A) the frequency equals the wavelength

B) the amplitude exceeds the wavelength

C) a wave's frequency is supersonic

D) a wave's period equals its wavelength

E) none of the above

22. An antinode is

A) always in the middle of a standing wave

B) a position of maximum amplitude

C) a position of minimum amplitude;

a node is a position of minimum amplitude (zero)

D) equal to the fundamental frequency

23. Light and sound are both waves. You may see bolt of lightning long before you hear its thunder. This is because

A) of resonance

B) light travels faster than sound

C) sound requires air to be transmitted and light does not

D) light passes through humid air but sound does not

24. A bobber on a fishing line oscillates up and down four times per second as waves pass by. The waves have a frequency of

A) (1/4) Hz

B) 4 Hz

C) (1/4) sec

D) 4 sec

25. A bobber on a fishing line oscillates up and down three times per second as waves pass by. The waves have a wavelength of 20 cm. The waves are traveling at

A) 20 cm/s

B) 40 cm/s

C) 60 cm/s

v = (frequency) x (wavelength)

v = ( 3 Hz ) x ( 20 cm)

v = 60 cm/s

D) 80 cm/s

26. If you put your fingertip in a pool of water and repeatedly move it up and down, you will create circular water waves that move out from that point. What will happen to the wavelength of these waves if you move your finger up and down more slowly (or less frequently)?

A) increase

v = (frequency) x (wavelength)

Decreasing frequency means increasing wavlength.

B) remain the same

C) decrease

27. Sound is

A) an electromagnetic wave

B) a polarized wave; only a transverse wave can be polarized

C) a longitudinal wave

D) all of the above

28. Light is or may be

A) an electromagnetic wave; light is always an EM wave

B) a polarized wave; because light is a transverse wave, it may be polarized

C) a transverse wave; light is always a transverse wave

D) all of the above

29. "Supersonic" means

A) lower than the range of human hearing

B) higher than the range of human hearing

C) faster than the speed of sound

D) slower than the speed of sound

30. "Ultrasonic" means

A) lower than the range of human hearing

B) higher than the range of human hearing

C) faster than the speed of sound

D) slower than the speed of sound

31. Bats and dolphins use echolocation to navigate or the find food or to find their way without relying on sight. The frequencies they use are

A) supersonic

B) infrasonic

C) ultrasonic

D) microsonic

32. If you double the frequency of a sound wave, you also double its

A) wavelength; if you double the frequency, you cut the wavelength in half

B) speed; the speed is independent of the frequency

C) amplitude; the amplitude and frequency do not depend upon each other

D) all of the above

E) none of the above

33. The range of human hearing is about

A) 10 Hz to 100 Hz

B) 50 Hz to 500 Hz

C) 50 Hz to 20 000 Hz

D) 1 000 Hz to 100 000 Hz

34. Sound travels fastest in

A) air (a gas)

B) water (a liquid)

C) aluminum (a solid)

D) vacuum

35. The speed of sound in air depends upon

A) wavelength

B) frequency

C) temperature

D) amplitude

36. Increasing the length of a vibrating string will

A) decrease its resonance frequency

Increasing the length means increasing the wavelength of the resonance and increasing the wavelength means decreasing the frequency

B) decrease its amplitude

C) increase its amplitude

D) increase its resonance frequency

37. Ella Fitzgerald made commercials for Memorex in which she used her voice to break a wine glass. This is an example of

A) echolocation

B) reflected sound

C) ultrasonic frequencies

D) resonance

38. Beats are heard when two sounds have

A) nearly the same amplitude

B) nearly the same frequencies

C) twice the amplitude

D) exactly twice the frequency

39. The fundamental frequency present in a sound is the

A) sum of all the frequencies mixed together

B) difference between the highest and lowest frequencies present

C) lowest frequency present

D) highest frequency present

40. The fundamental frequency present in a sound determines the

A) quality or timbre

B) amplitude or loudness

C) pitch or note

D) none of the above

41. The "pitch" of a sound is determined by its

A) overtones frequencies

B) harmonics frequencies

C) fundamental frequency

D) resonance frequencies

42. The quality or timbre -- the distincitive characteristic -- of a sound is determined by its

A) overtones or harmonics

B) amplitude or loudness

C) attack or decay

D) fundamental frequency

43. You hear beats with a frequency of 2 Hz when you strike a tuning fork that vibrates at 440 Hz and a chime. The chime has a frequency of

A) 440 x 2 Hz = 880 Hz

B) 442 Hz

The beat frequency is the difference in the two frequencies.

C) (440 / 2) Hz = 220 Hz

D) 110 Hz

44. The fundamental frequency of a violin string is 440 hertz. The frequency of its second harmonic is

A) 110 Hz

B) 220 Hz

C) 440 Hz

D) 880 Hz

45. Consider a musical note of 220 hertz ("A" below the staff). Two octaves higher is represented by a musical note of

A) 110 Hz; This is one octave lower.

B) 440 Hz; This is one octave higher.

C) 660 Hz

D) 880 Hz

46. The intensity or loudness of a musical sound is related to the sound wave's

A) wavelength

B) frequency

C) amplitude

D) wave speed

47. Suppose you play a note of a certain pitch on a violin. You can produce a higher-pitched note by

A) shortening the length of the string that is allowed to vibrate

B) decreasing the tension of the string (loosening the string)

C) increasing the linear mass density of the string (using a "heavier" string)

D) lengthening the part of the string that vibrates.

48. Consider the sound made when you blow across the open top of a soda bottle. Now pour some water into the soda bottle and again blow across the open top of the bottle. With the additional water now in the bottle, you should expect the pitch of the sound produced to be

A) higher

The additional water means the column of air which resonates is shorter.

This means the standing wave has a shorter wavelength.

And a shorter wavelength means a higher frequency.

B) lower

49. When a flute sound is viewed on an oscilloscope, the sound wave is very smooth. This is because

A) the amplitude is always small (flutes are quiet)

B) it has practically no overtones

C) its fundamental frequency has a smaller amplitude than its second and third harmonics

D) its harmonics get larger and larger

50. When a trumpet sound is viewed on an oscilloscope, the sound wave is very complex. This is because

A) the amplitude is always large (trumpets are loud)

B) it has practically no overtones

C) it has many overtones

D) its has only even-numbered overtones