1. What determines the frequency
17.2 Key Concepts
What determines the frequency
of a wave?
How are frequency, wavelength,
and speed related?
How is the amplitude of a wave
related to the wave’s energy?

2. Frequency and Period How do surfers know when the next wave is coming?
If they count the ________ between two successive
crests, the next crest usually will come after this same
_________________
Any motion that repeats at a regular
time intervals is called _____________
The time required for one cycle is called the ___________
time
interval
periodic
motion
period

3. Frequency and Period
Any periodic motion has a _________________, which is the number of wave cycles that pass a point in a given time.
Frequency is measured in __________________________ or ___________ (Hz).
Hz = 1/s
A wave’s frequency equals the frequency of the vibrating _________________ producing the wave.
frequency
cycles per second
hertz
source

4. A wave vibrating at one cycle per second has a frequency of ______.
Frequency and Period
Frequency = 1.0 hertz One cycle per second
A wave vibrating at one cycle per second has a frequency of ______.
A wave vibrating at two cycles per second has a frequency of _______
1.0 Hz
Frequency = 2.0 hertz Two cycles per second
2.0 Hz

5. Wavelength
Wavelength is the ______________ between a point on one wave and the same point on the _______ ____________ of the wave
distance
next
cycle
Long wavelength
Short wavelength
______________ the frequency of a wave _____________ its wavelength.
Increasing
decreases

6. Wavelength Which wave below has a higher frequency?
The second one (shorter wavelength)
Long wavelength
Short wavelength

7. Wavelength
For a transverse wave, wavelength is measured between adjacent _____________ or between adjacent _______________
crests
troughs

8. Wavelength
For a longitudinal wave, wavelength is the distance between adjacent _______________ or _________________.
compressions
rarefactions
Compression
Rarefaction
Compression

9. Wave Speed
If you assume that waves are traveling at a constant speed, then wavelength is ____________ proportional to frequency.
inversely

10. Wave Speed
When the wavelength is in ______________, and the frequency is in __________, the units for speed are _______________.
The speed of a wave is also calculated by dividing its wavelength by its ________________
meters
Hertz (1/s)
m/s
period
Speed = Wavelength
period

11. Speed of Mechanical Waves
Wave Speed
Speed of Mechanical Waves
One end of a rope is vibrated to produce a wave with a wavelength of 0.25 meter. The frequency of the wave is 3.0 hertz. What is the speed of the wave?
Speed =
0.25 m
x /s
= m/s

12. Wave Speed
1. A wave on a rope has a wavelength of 2.0 m and a frequency of 2.0 Hz. What is the speed of the wave?
Speed =
2.0 m
x /s
= 4.0 m/s

13. Wave Speed
2. What is the speed of a wave in a spring if it has a wavelength of 10 cm and a period of 0.2 s?
Speed = Wavelength
period
= _10 cm_
= 50 cm/s
0.2 s

14. Wave Speed
The speed of a wave can change if it enters a ______ ______________, or if variables such as _____________ and ______________ change.
new
medium
temperature
pressure

15. The more energy a wave has, the ____________ is its amplitude.
The amplitude of a wave is the _______________ _________________ of the medium from its rest position.
maximum
displacement
Low amplitude
High amplitude
The more energy a wave has, the ____________ is its amplitude.
greater

16. Amplitude
The amplitude of a transverse wave is the distance from the rest position to a crest or a trough.

17. Amplitude
The amplitude of a longitudinal wave is the maximum displacement of a point from its ________ position.
The more energy the
wave has, the more the
medium will be
compressed or
displaced.
rest
Rest position

18. Assessment Questions
1. True or False: Frequency is inversely proportional to wavelength.

19. Assessment Questions
What is the speed of an earthquake wave if it has a wavelength of 2.5 km and a frequency of 3 Hz?
7.5 km/s
5.0 km/s
2.5 km/s
1.3 km/s

20. Assessment Questions
The maximum displacement of a wave from its rest position is the ___________________.
period
frequency
wavelength
amplitude