Wave Terminology
- Wavelength(λ) is the distance between trough to trough, or crest to crest, or midpoint to corresponding midpoint.
- Amplitude(A) is the distance between the equilibrium point to either the trough or the crest.
- The period(T) and frequency(f) have an inverse relationship. (f = 1 / T)
Universal Wave Equation
v = λ X f
v = speed of wave (m/s)
λ = wavelength of wave (m)
f = frequency of wave (Hz or 1/s)
Longitudinal vs. Transverse Waves
- longitudinal waves: vibration of particles parallel to direction of wave propagation. ex) sound wave
- transverse waves: vibration of particles perpendicular to direction of wave propagation. ex) electromagnetic wave, water wave
For longitudinal waves, imagine that you are holding a spring and moving one hand from side to side. The wave will travel from left to right, and sections of the spring will also move from side to side. To describe the motion of longitudinal waves, we say that the vibration of particles and the direction of wave propagation are parallel.
For transverse waves, imagine that you are holding a rope and moving one hand up and down. The wave will travel from left to right, but sections of the rope will move up and down in this case. To describe the motion of transverse waves, we say that the vibration of particles and the direction of wave propagation are perpendicular.
Because the wooden ring oscillates perpendicular to the direction the wave travels, this water wave is a transverse wave.
If the distance from P to Q is is 5.0 cm, what is the amplitude of the wave?
The amplitude of a wave is the distance from the resting point to either the crest or trough. P to Q is twice of amplitude. Therefore, the amplitude of the wave is 2.5 cm.
If the wooden ring reaches point P every 15 s, what is the frequency of the wave?
T = 15 s
f = 1 / T = 1 / (15s) = 0.067 Hz
If the distance from one crest to the next crest is 20 cm, what is the speed of the wave?
λ = 20 cm = 0.20 m
v = λ x f = (0.20m) x (0.067Hz) = 0.013 m/s = 1.3 cm/s