PASCO WA-9867 Sine Wave Generator - Manual (Page 18)

Sine Wave Generator Standing Waves In Strings
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using a strobe light if one is available. Adjust the strobe frequency to be near the frequency of
the Sine Wave Generator. The string will look like it is moving in slow motion.
6. Try touching the string at an anti-node. What happens? Try touching the string at the central
node. Can you hold the string at the node and not significantly effect the vibration?
7. What was the wavelength when the string was vibrating in one segment? Use Equation 1 to
calculate the speed of the one-segment wave.
8. Calculate the speed of the two-segment wave. How do these to values compare? Are they
about the same? Why?
9. Adjust the frequency so that the string vibrates in three segments. Has the velocity changed?
Does the speed of the wave depend on the wavelength and the frequency?
Further Investigations
Changing Tension
1. Adjust the frequency so that the string vibrates in two segments. Now, without changing the
frequency, decrease the mass on the hanger until the string vibrates in 4 segments. (You may
have to use small masses to get a good waveform. Remember that it is more important to have
a good node at the end of the blade than to have the biggest amplitude possible.)
2. Record the total hanging mass, including the mass hanger. Calculate the ratio of the new mass
to the original mass. Why is the ratio not 2? You will learn more about the relationship
between wave velocity and string tension in Part II of this lab.
Changing Length
1. Return the mass to its original amount. Set the frequency to a value between the frequencies
that produced waves of two and three segments. Adjust the frequency so that no particular
standing waveform is present.
2. Unclamp the string vibrator and slowly move it towards the pulley. (Do not let go of the string
vibrator without clamping it to the table again.)
3. Without changing the driving frequency or the hanging mass decrease the length of vibrating
string until it vibrates in two segments. Adjust the position to get the best node at the blade, as
before. (If the hanging mass touches the floor, reattach it to the string higher up.)
4. Measure the new wavelength and calculate the speed of the wave. Is it about the same as
before? Does the speed of the wave depend on the length of the string?