Echo Time Calculation Using Oscilloscope Trace Steps: - Identify the time interval between the emission peak and echo peak from the diagram; it represents the round-trip time for the sound to the wall and back. - The oscilloscope sweeps the screen in 24 ms total; the peaks are positioned such that the interval corresponds to 9 ms (9/24 of the screen width). - The round-trip time is 9 ms, as this is the duration for sound to travel to the wall and return. - Divide the round-trip time by 2 to find the one-way time to the wall: 9 ms / 2 = 4.5 ms. Why A is correct: - The one-way travel time is half the measured interval between peaks, per the principle of echo reflection where distance = speed × time/2. Why the others are wrong: - B: Equals the full round-trip interval, ignoring the return journey. - C: Assumes the total screen time is the round-trip, but peaks show only 9 ms interval. - D: Exceeds the total screen time, impossible for the echo interval. Final answer: …