SHM
PHYS 1415 Lab-09: Beats
Name: _________________________
Objectives:
To use sound generation software to produce and observe the interference of multiple sound waves.
Discussion
When two sound waves interfere with one another, the resulting sound pattern is refe
ed to as beats. The beat pattern is determined by the waves that produce it. Piano tuners use knowledge of beats to tune pianos. A tuning fork with a key’s frequency is truck and the note is played. If beats are heard, an adjustment needs to be made. Land-line telephones send tones when keys are pressed. The tones are combinations of two notes played at the same time. Beats are all around us!
Procedure
1. Make sure the computer’s sound is on. If you use a pair of headphones, always make sure headphones/speakers are set to a low volume to avoid damage to hearing or equipment.
2. Open the website: https:
onlinetonegenerator.com
3. Default frequency is 440 Hz. You will hear a pure tone sine wave when you press “play” button.
4. You will see four different waveforms: Sine, Square, Sawtooth and Triangle. You will be using Sine waveform in this lab.
5. Open the same website in another tab or a new window. There should be 2 windows with the same website.
6. Play the frequency 440 Hz in both windows or tabs.
Question – 1: What do you hear when you play 440 Hz frequency in both tabs?
7. Using the frequency control slider, adjust one input wave to have a frequency of 440 Hz and the other to have a frequency of 441 Hz.
8. Listen for the beat frequency. The beat frequency is equal to the difference between the frequencies of the input waves. In this case, the beat frequency is 441 Hz – 440 Hz = 1.0 Hz. You should hear a 1.0 Hz “wah – wah” pattern in the resulting sound.
Question – 2: How else can you generate a 1.0 Hz beat frequency without changing the frequency of the 440 HZ input wave?
9. Adjust one input wave to have a frequency of 440 Hz and the other to have a frequency of 442 Hz.
Question – 3: Did the “wah – wah” pattern in the resulting sound change or remain the same?
10. Experiment with other combinations of input wave frequencies to create beats. Low frequencies produce interesting results.
Question – 4: What did you observe when changing frequencies to create beats?
Question – 5: What beat frequency is produced by 240-Hz and a 246-Hz tuning forks?
a) 6 Hz
) 240 Hz
c) 245 Hz
d) 12 Hz
e) none of the above
Question – 6: Suppose you sound a 1056-Hz tuning fork when you strike a note on the piano and hear 2 beats/second. You tighten the piano string very slightly and now hear 3 beats/second. What is the frequency of the piano string?
a) 1058 Hz
) 1059 Hz
c) 1054 Hz
d) 1053 Hz
e) 1056 Hz
2