சென்னையை காப்பாற்றும் கால் பந்து
5 Minutes
Doppler effect for students: discover how waves change frequency and how Chennai's radar detects cyclones. A Tamil science lesson.
- Wavelength and frequency with water waves and an ambulance siren
- How the Doppler effect alters sound pitch and shifts light colour
- How Chennai's radome radar tracks cyclone movement using microwaves
What this lesson teaches
The Doppler effect is the change in the observed frequency and wavelength of a wave when the source of the wave and the observer move relative to each other. When the source approaches, waves bunch together to produce a higher frequency, and when it moves away, waves stretch out into a lower frequency.
Waves, wavelength, and frequency
- Wavelength is the distance between two consecutive waves.
- Frequency is the number of waves that pass a fixed point in one second.
- When wavelength increases, frequency decreases, and when wavelength decreases, frequency increases.
- In sound waves, higher frequency creates a higher pitch, while lower frequency creates a lower pitch.
The Doppler effect in sound and light
When an ambulance stays stationary, its siren sends sound waves evenly in all directions at a constant pitch. When the ambulance moves towards an observer, the sound waves compress in front of it, shortening the wavelength and raising the frequency to produce a sharper pitch. As the vehicle travels away, the sound waves behind it stretch out, creating a lower frequency and a deeper tone. The same effect happens with electromagnetic waves, where moving fast enough towards an observer shifts light to higher frequencies, which could theoretically shift red light into green light.
How Chennai tracks cyclones
The large football-shaped structure seen near Chennai's Marina Beach is a weather dome called a radome, which shields a radar antenna. This radar transmits microwave beams into the sky at a specific frequency. When these microwaves hit rain clouds or an incoming cyclone, the waves reflect back towards the radar station. If the cyclone is moving towards the city, the returning waves arrive at a higher frequency due to the Doppler effect, and if the cyclone is moving away, the frequency drops. This frequency shift allows meteorologists to calculate the exact direction and movement of dangerous storms well in advance.
Other uses of the Doppler effect
- Bats use high-frequency sound reflections and the Doppler effect to locate and catch flying prey in the dark.
- Radar systems in autonomous cars use Doppler wave reflections to detect moving obstacles and prevent collisions.
- Human echolocation relies on reflected sound vibrations to identify moving obstacles and track surroundings without sight.