Practice Problem 0505
The two sources in the above figure were vibrating for a total of 0.9 seconds. Determine
a) the frequency of the sources
b) the wavelength
c) the speed of the waves
Crests
Troughs
S1
Focusing only on one of the sources, to determine the frequency of the source, count the total number
of cycle created.
Begin by counting one cycle at a time. One full cycle consists of either a crest-trough-crest
combination or a trough-crest-trough combination
S1
Based on the figure, there are 4 full waves and half a wave leftover. Therefore, there are 4.5 waves in
total.
Hence, frequency is number of cycles over total time
4.5 cycles/0.9 seconds = 5 Hz
For the wavelength, measure the distance from crest to crest or trough to trough.
wavelength is 0.8 cm.
For speed, we can use the wave equation.
Speed = (frequency)(wavelength) = 5(0.8) = 4 cm/s.