Cracking the SAT Physics Subject Test

The simple equation v = λf shows how the wave speed, wavelength, and

frequency are interconnected. It’s the most basic equation in wave

theory—know it for the test.

1. A traveling wave on a rope has a frequency of 2.5 Hz. If the
   speed of the wave is 1.5 m/s, what are its period and wavelength?

Here’s How to Crack It

The period is the reciprocal of the frequency.

The wavelength can be found from the equation λf = v.

2. The period of a traveling wave is 0.5 s, its amplitude is 10 cm,
   and its wavelength is 0.4 m. What are its frequency and wave
   speed?

Here’s How to Crack It

The frequency is the reciprocal of the period: f = 1/T = 1/(0.5 s) = 2 Hz. The wave
speed can be found from the equation v = λf.

v = λf = (0.4 m)(2 Hz) = 0.8 m/s

(Notice that the frequency, period, wavelength, and wave speed have nothing to do
with the amplitude.)