http://www.ck12.org Chapter 12. Waves and Energy Transfer
Another important characteristic of a wave is its velocity. The wave velocity is different from the velocity of the
medium; the wave velocity is the velocity of the linearly transferred energy. Since the energy travels one wavelength,
λ, in one period,T, the velocity can be expressed as distance over time:
v=
λ
T.
Since period and frequency are reciprocals, the speed of the wave could also be expressed asv=λf.
Example Problem:A sound wave has a frequency of 262 Hz. What is the time lapse between successive wave
crests?
Solution: The time lapse between successive crests would be the period and the period is the reciprocal of the
frequency.
T=
1
f=
1
262 s−^1
= 0 .00382 sExample Problem:A sound wave has a frequency of 262 Hz has a wavelength of 1.29 m. What is the velocity of
the wave?
Solution:v=λf= ( 1 .29 m)(262 s−^1 ) =338 m/s
Summary
- Mechanical waves require a material medium such as water, air, or rope.
- In all types of mechanical waves, energy moves from one place to another while the media carrying the wave
only vibrates back and forth in position. - One type of mechanical wave is the transverse wave, in which the movement of the medium is perpendicular
to the direction of the energy propagation. - The maximum displacement of the medium is the distance from the undisturbed position to the top of a crest,
or the amplitude. - The distance along the line of motion of the wave from equivalent positions on succeeding waves is the
wavelength. - The time interval required for one entire wave to pass a point is the period.
- The number of periods per second is the wave’s frequency.
- The period of a wave and its frequency are reciprocals of each other.
- The velocity of the wave’s energy transfer is given byv=λfor
v=λ
T.
Practice
Questions
The following video explains wave characteristics. Pause the video before each practice question and try to solve it
yourself before moving on.