The Doppler effect is a phenomenon where the frequency of a wave changes for an observer when there is relative motion between the source of the wave and the observer. It applies to all types of waves, including sound, light, and radio waves.
How It Works:
- When the source of the wave moves toward the observer, the waves are compressed, leading to a higher frequency (or pitch, in the case of sound).
- When the source moves away from the observer, the waves are stretched, resulting in a lower frequency.
This change is not because the actual frequency emitted by the source changes, but because the relative motion alters how the wavefronts are received.
Everyday Examples:
- Sound of a passing ambulance: As it approaches, the siren sounds higher in pitch. As it passes and moves away, the pitch drops.
- Radar guns: Used by police to detect speeding vehicles, based on the Doppler shift in reflected radio waves.
- Weather radar: Detects the movement of raindrops to measure wind and storm patterns using Doppler shifts in radio waves.
Doppler Effect in Light:
- In astronomy, the Doppler effect explains the redshift and blueshift of light:
- Redshift occurs when distant galaxies move away from us, causing light to stretch toward longer, redder wavelengths.
- Blueshift happens when an object moves closer, compressing the light to shorter, bluer wavelengths.
Why It’s Important:
The Doppler effect is essential for:
- Measuring the speed and direction of objects.
- Understanding the expansion of the universe.
- Designing navigation systems like sonar and radar.