Question
7. [1pt]
A long metal rod of length L, 1/2 inch in diameter, isheld between the fingers. It is hit on one end with a small hammer.It resonates, emitting sound with a frequency of 6640 Hz. Theamplitude of the oscillations along the bar is shown qualitativelybelow. What is the harmonic number of the normal mode illustrated?You have only 2 tries!
Answer:
8. [1pt]
The speed of the wave is 5200 m/s. Calculate the lengthL of the rod.
Answer:
9. [1pt]
Referring to the mode above, answer T-True, F-False. E.g., if thefirst is T and the rest F, enter TFFF.
Answer:
7. [1pt] A long metal rod of length L, 1/2 inch in diameter, isheld between the fingers. It is hit on one end with a small hammer.It resonates, emitting sound with a frequency of 6640 Hz. Theamplitude of the oscillations along the bar is shown qualitativelybelow. What is the harmonic number of the normal mode illustrated?You have only 2 tries! The speed of the wave is 5200 m/s. Calculate the lengthL of the rod. Referring to the mode above, answer T-True, F-False. E.g., if thefirst is T and the rest F, enter TFFF. The wave in the rod is longitudinal. The rod will resonate if the fingers are 1/4 L fromone end. The wave's speed will not change if L isdecreased. The frequency of that mode will decrease if L islengthened.
Explanation / Answer
harmonic number is the number of half wavelengths. You have,by the diagram . 1/4 1/2 1/2 1/2 1/4 = four half wavelengths . So harmonicnumber = 4 . (b) wavelength = speed / freq = 5200 / 6640 = 0.783133 meters . The rod has a length of four half wavelengths ,or two wavelengths... so . L = two wavelengths = 2 *0.783133 = 1.566meters (c) The true false are T F T T, although the second one might betrue... so it couldbe T T T T . The second question is a bit ambiguous... it doesnt give anyspecifics of the resonance of the rod.