Waves Review Sheet Answers
1. Transverse and longitudinal waves are both types of waves and, therefore, both
exhibit wave properties (reflection, refraction, interference, etc.). They are different
terms of the direction of motion of the medium and the direction of motion of the
wave. In transverse waves, the medium moves perpendicularly to the direction of
the wave itself (e.g., waves in water, waves on a taut string). In longitudinal waves,
the medium moves parallel to the direction of the wave itself (e.g., sound waves).
2.
constructive
destructive
3. In terms of waves, the
superposition (interference)
principle states that when multiple waves pass through each other, the resulting
combination of these waves in the sum of the individual amplitudes at a given
position in space and time. More succinctly but less accurately, add up the
amplitudes of the waves.
4. Period is the time for the medium to complete one cycle of a wave (seconds for each
cycle). Frequency is the number of cycles of a wave that pass a given point in one
second (cycles for each second). Period and frequency are reciprocals of each
other. Wavelength (λ) is the length of a single cycle of a standing wave (e.g.,
distance between two crests). Amplitude is the distance from the equilibrium
position to the maximum displacement of the medium (e.g., distance from
equilibrium position to crest).
5.
6. v = f λ (v: m/s; f: cycles/s; λ: m)
7. v = f λ
(50.0 cm/s) = f (5 cm)
f = 10 Hz = 10 cycles/s
8. Sound is a longitudinal wave that travels fastest in mediums where the molecules
that comprise the medium are very elastic. Sound travels faster in a steel pipe than it
does in water. Sound travels faster in water than it does in air.
9. The pitch of a note depends on the frequency of the sound wave and the loudness
and intensity depends on the amplitude of the sound wave. For mechanical waves,
amplitude is proportional to the energy transferred by the wave.
10. When two standing sound waves of similar but not identical frequencies interfere,
they produce beats. The frequency of the beats is equal to the difference in
frequencies of the two waves.
11. Compared to a stationary sound source, as an observer of a sound source that is
moving away from you, you observe its wavelength getting longer and its frequency
getting less. Therefore, the sound goes down in pitch. This is called the Doppler
Effect. (The opposite effect is observed when the relative motion of the sound
source and the observer is towards each other.)
12. Resonance is the natural frequency of a vibrating object. Resonance is created
when an external force is applied at the natural (resonant) frequency. A standing
wave (e.g., any musical tone) is an example of resonance.
13. The Law of Reflection states that the angle of incidence equals the angle of
reflection.
14. Refraction is the bending of a wave when it crosses between two mediums in which
it travels at different speeds. The normal is a line perpendicular to a surface at a
point.
15. When light pass through a denser medium such as glass or water (as compared with
air), it slows down.
16. The index of refraction for a medium is the ratio of the speed of light in a vacuum to
the speed of light in that medium (n = c / v). For all mediums other than a vacuum,
the index of refraction is greater than 1.
17. When light goes from a more-dense medium to a less-dense medium, it bends away
from the normal. When light goes from a less-dense medium to a more-dense
medium, it bends towards the normal.
18.
Snell’s Law: ni sinΘi = nr sinΘr
nair sinΘi = nglass sinΘr
(1.00) sin(37°) = (1.52) sinΘr
Θr = 23°
19. ni sinΘi = nr sinΘr
nplastic sinΘi = nair sinΘr
nplastic sin(25°) = (1.00) sin(32°)
nplastic = 1.25