Physics 101 LO8

1. Beats
Physics 101 LO 8
Selina Lo #33096132

2. What is a beat?
• The result of constructive and destructive interference that
causes 2 waves to have difference frequencies, causing
the amplitude to increase and decrease over a function of
time.
• Beat frequency = the absolute value of the difference in
frequency of 2 waves.

3. Beat envelope
• Let sine wave represents a single frequency with
constant amplitude
• Beat envelope: 2 waves of slightly different frequencies
are added, the resulting amplitude will vary or oscillate
at a rate that is the difference between the frequencies.
Created around original sine wave.

4. Resulting wave equation
Beat envelope is the resulting wave

5. Examples
Question: Calculate the beat frequency if the two frequencies of
waves are 750Hz and 380Hz respectively?
Answer:
f1 = 750Hz and f2 = 380Hz
The beat frequency is given by,
fb = |f1−f2|
fb = |750−380| = 370Hz

6. Examples
Question: A tuning fork with a frequency of 440 Hz is sounded
together with a note played on a piano. Eight beats are heard in 2
seconds. What is the frequency or pitch of the piano note?
Answer: Beat frequency = 8 beats = 4 Hz
2 secs
fb = |f2−f1|
4Hz = |440−f1| = 444Hz or 436 Hz

7. References
• Hawks, R.,Iqbal, J. Mansour, F, Milner-Bolotin, M. & Williams P.
2014. Physics for Scientists and Engineers: An Interactive
Approach (1st ed.) Nelson Education Ltd.