1. Beats

2. Beats
Beats are a special case of interference where two tones of slightly different frequencies are heard together.
The vibration of the forks will vary in and out of step, causing both constructive and destructive interference

3. Beats
The two sound waves and their slightly different frequencies will add into a new wave by the principle of interference
This new wave will fade in and out as the two original waves go in and out of phase

4. Beats
Video on beats

5. Beats
To find the frequency of the beats, you need the difference between the two frequencies creating the beats
f1 = 230Hz and f2 = 233Hz. The frequency of the beats will be |f1 – f2| = |230Hz – 233Hz| = 3Hz

6. Beats
When the waves are in phase, the resulting wave has a maximum amplitude, and the beat frequency is the loudest
When the waves are out of phase, the resulting wave has a minimum amplitude, and the beat frequency is not heard.

7. Sound Pressure Sound level is measured in decibels (dB)
Sound level depends on the ratio of the pressure of a given sound to pressure of the most faintly heard sound (0 dB)
Every time the decibels increases by 10, the sound level is multiplied by a factor of 10
So the difference between 20 and 10 dB in sound level is 10, and 30 to 10 dB is 100

10. Beats and Sound Pressure
Do the two problems on the worksheet
Then hw is page 402 # 19, 20, 27, 36, 37