Lecture 94: The Doppler Effect

In this video, I discuss the wave phenomenon known as the Doppler shift. You've likely experienced the Doppler shift with sound waves if you've noticed how the pitch of an approaching car horn changes as it passes by. I begin by explaining how the frequency increases and the wavelength decreases for a moving source of waves. Conversely, for a receding source, the frequency decreases and the wavelength increases. When the wave source is stationary and the observer moves, the wavelength remains unchanged, but the frequency increases or decreases depending on the observer's direction.
This scenario suggests that the Doppler shift for light waves could potentially determine absolute motion. However, this dilemma is resolved by considering the relativistic Doppler shift, which takes into account the principles of relativity.
Next, I discuss the Cerenkov cone that forms when the wave source exceeds the wave speed. I conclude with a bit of my own research, illustrating an intriguing effect of a reverse Cerenkov cone that occurs in negative refractive materials. Through these discussions, viewers will gain a comprehensive understanding of the Doppler shift and its implications in both classical and relativistic contexts.