Passage III

Two students were each asked to experimentally determine the speed of sound in air, s_a. For the atmospheric conditions in which their experiments were performed, the correct value of was s_a 347.1 m/sec.

Experiment 1

Student 1 placed a horn, which could emit a short pulse of sound waves, at a distance x, in m, from a tall cliff (see Figure 1).

He started a stopwatch when he heard the horn emit a sound pulse and stopped the stopwatch when he heard an echo return from the cliff. He recorded this time interval, Δt₁, in sec, and then calculated s_a, using the equation

Student 1 performed 3 trials at each of 3 values of x, averaging the s_a results at each value of x (see Table 1).

Experiment 2

Student 2 placed the horn and 2 microphones—M₁ and M₂—in a straight line such that the microphones were separated by a distance y. She then connected a timer to both microphones (see Figure 2).

She set the timer to start when the first microphone detected a sound pulse and to stop when the second microphone detected a sound pulse. She recorded this time interval, Δt2, and then calculated s_a using the equation

Student 2 performed 3 trials at each of 3 values of y, averaging the s_a results at each value of y (see Table 2).