12.1. Transverse Waves http://www.ck12.org
In the sketch above, consider the transverse wave produced when the boy jerks one end of a rope up and down while
the other end is tied to a tree. The energy spent by the boy transfers permanently down the rope to the tree. The
rope, however, only moves up and down. If we stuck a piece of tape somewhere on the rope, we would see that the
particles of medium do not travel with the energy. After the wave has passed by, the piece of tape would still be in the
same place it was before the wave approached. In all transverse waves, the movement media vibrates perpendicularly
to the direction of wave motion, and the medium is not permanently moved from one place to another.
Frequency, Wavelength, and Velocity
Waves are identified by several characteristics. There is a center line where the medium would be if there were
no wave, which is sometimes describes as the undisturbed position. The displacement of the medium above this
undisturbed position is called acrestand the displacement below the undisturbed position is called atrough. The
maximums of the crest and trough are equal and are called theamplitude. The distance between equivalent positions
on succeeding waves is called thewavelength. The wavelength could be measured from a crest to the next crest or
from a trough to the next trough, and is commonly represented with the Greek letter lambda,Ī».
The time interval required for one complete wave to pass a point is called theperiod. During the period of the wave,
an entire wavelength from one crest to the next crest passes a position. The number of waves that pass a single
position in one second is called thefrequency. The period of a wave and its frequency are reciprocals of each other.
f=1
T
The units for the period are seconds and the units for frequency are sā^1 or^1 s. This unit has also been given the name
Hertz (Hz).