AP Physics Experiment Law of Strings Purpose To determine the relationship between frequency, tension, and string length. Procedures 1. Measure and record the mass (M) in kg of the sonometer wire. 2. Stretch the heavier of the two wires on the sonometer with a load of approximately 1kg if available. 3. Measure and record the frequency (f) in Hertz of the tuning fork. 4. Measure and record the total attached mass (m). Calculate the tension (T) in the string equal to mg. 5. Calculate the tension to yield the selected frequency using the equation T = 4MLf2. 6. Add mass to the hanger to produce the calculated tension in the wire. 7. Set the tuning fork vibrating by striking it with a rubber mallet. Place the base of the tuning fork in contact with the top surface of the sonometer. 8. Pluck or strum the string with a bow and make any adjustments in the bridge until there is a match between the fundamental frequency of the sonometer string and the tuning fork. Record the length (L) of the wire to the bridge in meters. 9. Calculate the frequency of the string (fs) using the formula fs=(1/[2L])[(TL)/M)]. 10. Repeat steps #1-9 using the lighter sonometer wire with a tuning fork of higher frequency if possible. Data
Wire
Vibrating String Length (L) (meters)
Load (kg)
Calculated Tension (T) (N)
Mass of Wire (M) (kg)
Frequency Frequency Calculated Measured (f) (f) (Hz) (Hz)
Heavier Lighter
Analysis The following points should be addressed in the analysis:
How is a standing wave formed in a string? What is the nature of harmonics in a string? What factors could account for any variations between the calculated and actual values for the frequencies? What is the relationship between resonance and beat frequency? What factors influence the harmonics possible in the wire?
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