A student puts a pulsed laser and detector in the hall of the chemistry building. She places a mirror at the other end of the building and measures the roundtrip distance at 312 ft 6 in. She calibrates a time-measuring device called an oscilloscope, which records the amplitude of the laser signal as a function of time. The results of two experiments, in which the vertical axis shows the magnitude of the signal and the horizontal axis shows the time, are shown. The first peak indicates the moment at which the laser fired, and the second peak is due to the pulse returning from the mirror.

Measuring the velocity of light.

(a) Calculate the velocity of light in both experiments. Use the convention of significant digits to express the uncertainty.

(b) Explain what factors limit the uncertainty. In other words, how can the student improve the experiment?

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Laser signal 1.2 1.0 0.8 0.6 0.4 0.2 0 100 200 300 Time (ns) 400 500