8 4 Determining Wave Speed The Universal Wave

8. 4 – Determining Wave Speed

The Universal Wave Equation Recall: to find speed, v = d t For a wave, d = length of wave, λ t = time for one cycle, T v=λ T or v = λf (since 1/T = f)

Things to Note: �One vibration/cycle of the source → one complete wavelength. �the frequency of the source = The frequency of the wave �If the frequency of the source never changes then the frequency of the wave doesn’t either, even if the speed and wavelength change. �Speed and wavelength can change due to a medium change

Example 1 The wavelength of a water wave in a ripple tank is 0. 080 m. If the frequency of the wave is 2. 5 Hz, what is its speed?

Example 2 The period of a sound wave from a piano is 1. 18 x 10 -3 s. If the speed of the wave in the air is 3. 4 x 102 m/s, what is its wavelength?

Factors That Affect Wave Speed Temperature �In gases, higher temp = more efficient transfer of energy because molecules are vibrating faster Linear Density �Mass/unit of distance → determines amount of force needed to make string vibrate µ=m m – mass (kg) L L – length (m)

Factors That Affect Wave Speed �

Example 3 If a string on a wave machine has a linear density of 0. 011 kg/m and a tension of 250 N, what is the wave speed?

Example 4 If a 2. 5 m long string on the same wave machine has a tension of 240 N, and the wave speed is 300 m/s, what is the mass of the string?

Homework pg 391 #1 - 7 Quiz on Wednesday