Physics : Beats

1. Beats
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Poramat Sucharit 31771141

2. What is ‘Beats’
• ‘Beats’ are formed when two waves with different
frequency approaches your ear.
• The sounds constructive and destructive interference
causes the sound to be alternatively soft and loud.

3. Beats formula
• The number of beats per second is equal to
the difference in frequency.
•

4. Beats
• Beats are created from the interference of two waves
that are very close to each other, creating a higher and
smaller amplitude in different region.
• Beat Period is define by the distance between the two
maximum amplitudes.

5. General Formula
• Fb = Beat Frequency
• F1 and F2 = Two sound frequency
• |F1 – F2| = Absolute value (Always postive)

6. Example
• If there are two waves with frequency of
330Hz and 350Hz.
– The resulting frequency will be the average of the
two waves. (330+350)/2 = 340 Hz
– The beat frequency will equal to Fb =|F1 – F2|,
therefore Fb = |330-350| = 20 Hz

7. Question 1
• If your tuning your piano, and you tighten the
piano spring to 450 Hz. You notice that the
beats of 2 Hz remains the same. What was the
frequency of the piano note before you
tighten the string.

8. Answer
• Fb =|F1 – F2|
• Fb = 450 Hz – 2
= 448 Hz
*When the string is tighten, the velocity and
frequency of the waves must have increased.

9. Question 2
• A tuning fork with a frequency of 430 Hz
sound together with a note played on a guitar,
10 beats are recorded in 3 seconds. What is
the frequency of the guitar note?

10. Answer
• Fb =|F1 – F2|
• Find the beats frequency
– 10 Beats / 3 sec = 3.33
• Then apply the formula
– 3.33 Hz = |430 Hz – F2|
– = 433.33 Hz or 426.67 Hz
– * This is because of the absolute sign ‘||’ the
answer will always be positive, thus two answers.