Passage VII
A student conducted experiments to determine the relationship between the musical pitch (frequency) of a vibrating string and its length, tension, and mass density (mass per unit length of string).
Experiment 1
The student cut several lengths of steel strings having different diameters. The strings were weighed and their mass densities calculated. Specified lengths of the strings were hung from the ceiling. A block was suspended from the free end of each string, making the tension in the string equal to the suspended weight in newtons (N). Plucking the string caused it to vibrate, producing sound waves. The sound waves were detected by a microphone and displayed on the screen of an oscilloscope, where the fundamental frequency of vibration, in cycles per second, or hertz (Hz), could be measured. The results are presented in Table 1.
Experiment 2
The student repeated the procedure in Experiment 1, using strings made of nylon and gut and having different diameters. The results are presented in Table 2.
35. The variable that is directly manipulated by the student between Trials 10 and 11 is the:
Your Answer is
Correct Answer is D
Explanation
According to Table 1, the two options AC are the same in the two trails, so the students must have not operated it. The vibration frequency of option B cannot be directly controlled by humans. It can only be changed by different weights that lead to different rope tension , so choose D.