The Doppler Effect (in motion)
The Doppler Effect, named after Austrian Christian doppler in 1842, is a fundamental concept in physics that explains how the frequency or wavelengths of a wave, whether it’s sound or electromagnetic radiation changes when with either the source or the observer is in motion relative to each other. For a stationary sound source emitting a constant-frequency wave, all observers perceive the same frequency because the wavefronts maintain a fixed separation. Consequently, the wavelength and frequency remain unchanged. However, when the source is in motion relative to an observer, the frequency of the sound waves received by the observer will be different from the frequency at which the source emits sound in a stationary state. If the source approaches the observer, the observed frequency increases (high pitch for sound, and ‘blueshift’ for light). Moving away however, the observed frequency decreases (lower pitch for sound or ‘redshift for light’). This frequency shift can be calculated using the Doppler Effect Equation:
fo=fs v/(v±vs )
fo is the observed frequency
fs is the actual frequency
v is the wave velocity
vs is the source velocity
The (+) or (-) sign depends on whether the source is moving toward or away from the observer.
Overall, the Doppler Effect mathematically explains how we perceive different pitches of sound or shifts in light frequencies based on relative velocities. It has applications in astronomy, meteorology, diagnosing medical conditions through Doppler ultrasound, and detecting galaxies motion. Understanding this effect is crucial for unravelling the dynamics of waves in the physical world.
— Callum Alexander (S6)