Two ultrasonic transducers, the receiver stationary at the end on a linear air track, and the source mounted on a moving glider, are the basis for a Doppler shift experiment. The source frequency and the shifted receiver frequency are fed into a digital phase detector circuit which produces an output difference frequency with a sinusoidal waveform. This Doppler shift frequency can be measured directly and compared with the shift predicted from theory.
Coherent signal detection techniques are applied to conventional ultrasonic pulse-echo measuring apparatus to achieve a 20–25 dB improvement in the minimum useful signal. Logic circuitry is described which generates all the reference and trigger waveforms required by the sampling oscilloscope, lock-in amplifier, and other equipment. No other pulse generators are required. Amplitude adjustment of the pulsed rf comparator is determined to be equal that of the echo by a null indication of the lock-in voltmeter.
Over the past several years, we have contributed articles to TPT that focus on a forensics-style reexamination of significant historical events. The purpose of these articles is to afford students the opportunity to apply basic principles of physics to unsolved mysteries and potentially settle the historical debate. We assembled the lessons learned and best practices of our activities into a formalized pedagogy for teaching topics in physics, engineering, problem solving, critical thinking, and ethics.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.