Waves and Sound Study Guide Answer Key
1. Waves carry ___energy_____ (energy, matter), the do not carry ____matter____ (energy, matter).
2. What are the two categories of waves?
a. Electromagnetic and Mechanical
3. What are the two types of waves?
a. Transverse and Longitudinal
4. Why are mechanical and electromagnetic waves similar?
a. They both carry energy and can travel through a medium
5. Why are mechanical and electromagnetic waves different?
a. Mechanical waves require a medium while EM waves do not
6. Draw a transverse wave. Label the crest, trough, rest position, wavelength and amplitude.
7. Draw a longitudinal wave. Label the compression, rarefaction and wavelength.
8. What happens to the frequency of a wave if the wavelength is increased?
a. Frequency will decrease
9. Calculate the speed of a sound wave if the wavelength is 57 cm and the frequency is 250 Hz.
a. v = λ * f
v = 57cm * 250 Hz v = 14,250 cm/s
10. What is the difference between constructive interference and destructive interference?
a. Constructive interference is when a crest overlaps with a crest or a trough overlaps with another trough.
This results in a larger amplitude, and if it is a sound wave it will make a louder sound.
b. Destructive interference is when a crest overlaps with a trough, resulting in a smaller amplitude. If this
were a sound wave, it would make a softer sound. If the two waves have the same amplitude, it will
result in total destructive interference and the new amplitude will be 0.
11. Which wave would have more energy; a wave with a small amplitude or a wave with a large amplitude
(assuming they have the same wavelength)?
a. A large amplitude
12. What is the difference between reflection and diffraction?
a. Reflection is when a wave bounces off of an object, while diffraction is when a wave bends around a
barrier or through an opening.
13. If a singer sings a long, high note and a glass on the table next to them breaks, this is caused by what?
a. Resonance
14. What are the two factors that affect the speed of sound?
a. Medium and temperature. Sounds travel faster through solids than gases. Sound also travels faster at
higher temperatures and slower at lower temperatures.
15. What is the difference between infrasonic sound waves and ultrasonic sound waves?
a. Infrasonic sound waves are below 20 Hz and ultrasonic sound waves are above 20,000 Hz
16. What are two ways uses of ultrasonic sound waves?
a. Breaking apart kidney stones, cleaning jewelry, cleaning teeth. All of these use ultrasonic sound waves
along with resonance.
17. If an ambulance is driving away from you, the siren will sound lower in pitch than when it was traveling toward
you. Why is this true?
a. The siren sounds lower in pitch because of the Doppler Effect. As the ambulance drives away from you,
this causes the sound waves to be spread farther apart, resulting in a lower frequency and therefor a
lower pitch.