Waves Practice 5
Name ____________________
1. A 2 meter long string is tied at both ends, so that the ends can’t move. A motor which can
produce a varying frequency is used to vibrate the string.
a. What are the wavelengths of the first, second and 4th harmonic?
b. If the frequency of the 3rd harmonic is 420 Hz, what are the frequencies of the 1st, 2nd
and 4th harmonics?
c. What is the speed of the wave in the string?
2. A 4 meter long tube is a “closed one end” oscillator, used to produce sound with different
frequencies. The speed of sound is 340 m/s.
a. What is the wavelength of the fundamental, the 3rd harmonic and the 5th harmonic?
b. What is the frequency of the fundamental, the 2nd and the 3rd harmonic?
3. The frequency of the 3rd harmonic of an “open both ends” oscillator is 270 Hz. What is the
frequency of the 5th harmonic?
4. What is the ratio of the frequencies of the 4th harmonic to the 3rd harmonic of a closed both
ends oscillator? What is the ratio of their wavelengths?
5. In the box below, I’ve drawn the first harmonic of an open both ends oscillator. In the other two
boxes, sketch the 2nd and 5th harmonic. Find the wavelength of each.
6. A lab is performed like the one we did in class. A tuning fork with an unknown frequency is held
above a tube. The water level in the tube can be lowered or raised. The sound was loudest when
the water level was at positions L1, L2, and L3.
a.
b.
c.
d.
What is the phenomenon which caused the sound to be louder at those positions?
If L1 = 14 cm, and L2 = 60 cm, what was the wavelength of the sound wave?
Assuming the speed of sound is 340 m/s, what is the frequency of the tuning fork?
What is the position of L3?
7. .