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Lab 12.3 Natural Frequency and Resonance. Setting up the experiment. Plug in the AC adapter to turn on the equipment—everything is already wired. Set the timer to frequency ; set the wave generator to waves.
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Setting up the experiment • Plug in the AC adapter to turn on the equipment—everything is already wired. • Set the timer to frequency; set the wave generator to waves. • The Wiggler should start to wiggle the dark blue string back and forth. The number on the timer display should read about 10, meaning that the wiggler is moving 10 times in 1 sec (10 Hz).
Try this out • Turn the frequency knob on the wave generator clockwise and watch the display on the timer. The more you turn, the higher the number. • While you are turning the knob, watch the pattern of the vibrations on the string.
Get some data • Copy the following table into your lab notebook. Harmonic # f (Hz) λ (m) f times λ 1 2 3 : 10 +
Data, continued • At certain frequencies, the vibrating string will form wave patterns like . The patterns are called harmonics. The 3rd harmonic has 3 lemon shapes. You will experiment with the Wiggler to find the frequencies of the first 10 harmonics. Start with 3 and go up. Find 1st and 2nd last (easier that way!)
Data • Fine-tune the frequency to obtain the largest amplitude before recording the data for each harmonic resonance. • To get you started, the 3rd harmonic is found between 20-26 Hz on your Wigglers. • DO NOT go above 125 Hz on your wave generators!
If you have time… • Try to find the 11th, 12th, 13th harmonics. Copy the frequencies in your notebooks.
How to find wavelength (λ) • The wavelength of each harmonic is the length of one complete wave. • One complete wave is 2 bumps (lemons). • Therefore, one wavelength is the length of two bumps. • The string is 1 meter long. • Record your wavelengths as FRACTIONS of a meter.
f x λ • Multiply the frequency in Hz by the wavelength. • Do you notice a pattern?
Follow-up Questions • Obtain a half-sheet question sheet from your teacher. • The answers should be typed. • The due date for the lab questions is Monday, 5/2