traveling waves
Summary
A traveling wave is a disturbance that carries energy through a medium (or, for light, through space) while the medium's particles only oscillate about fixed positions. Its speed follows v = fλ and is set by the medium; the source sets the frequency.
Detail
Meaning: A traveling wave is a disturbance that moves from place to place, transferring energy. The particles of the medium oscillate about their equilibrium positions and are not carried along with the wave. In a transverse wave the oscillation is perpendicular to the direction of travel (waves on a string, light); in a longitudinal wave it is parallel (sound). A standing wave differs: its pattern stays in place, with fixed nodes and antinodes and no net energy transfer along the medium. Electromagnetic waves are traveling waves that need no medium.
Equation: v = fλ, where v is wave speed (m/s), f is frequency (Hz, or s⁻¹), and λ is wavelength (m).
On the MCAT: A common setup is a wave crossing into a new medium. The frequency stays the same, so speed and wavelength change in proportion. Speed depends on the medium: tension and linear density on a string, and for light the index of refraction (n = c/v). Sound generally travels faster in solids than in gases. Other questions ask you to read a displacement-versus-position or displacement-versus-time graph for λ or period, or to note that intensity rises with the square of the amplitude.
Common confusion: Students think a higher frequency makes a wave travel faster, or that the medium's particles travel with the wave. The medium sets the speed, and the source sets the frequency. Raising f at fixed speed shortens λ.
Sources
- Physics (Cutnell and Johnson)
- University Physics (Young and Freedman)
- Fundamentals of Physics (Halliday, Resnick, and Walker)
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.