The scattering of light by colloidal particles making the path of light visible
What is Tyndall Effect?
The Tyndall effect is the scattering of light by particles in a colloid or fine suspension. Named after physicist John Tyndall, this phenomenon makes the path of light visible through otherwise transparent mediums.
Examples in Daily Life
π Sunbeam in a Dusty Room
When sunlight enters through a small window in a dusty room, you can see the path of light as dust particles scatter the light.
π² Light Through Forest Canopy
Sunlight filtering through trees becomes visible due to tiny water droplets and particles in the mist.
π Car Headlights in Fog
The beam of headlights becomes visible in foggy conditions due to water droplets scattering the light.
| Medium | Particle Size | Tyndall Effect | Example |
|---|---|---|---|
| True Solution | < 1 nm | Not Visible | Salt water |
| Colloidal Solution | 1 nm - 1000 nm | Visible | Milk, fog |
| Suspension | > 1000 nm | Very Visible | Muddy water |
Understanding Rayleigh scattering and atmospheric optics
The Science Behind Blue Sky
The blue color of the sky is due to Rayleigh scattering. Air molecules and tiny particles in the atmosphere scatter short-wavelength light (blue and violet) more than long-wavelength light (red and orange).
Key Facts:
- Blue light has wavelength β 450 nm
- Red light has wavelength β 700 nm (1.8Γ longer)
- Scattering intensity β 1/Ξ»β΄ (inversely proportional to wavelengthβ΄)
- Blue light is scattered ~5 times more than red light
Why Not Violet?
Although violet light scatters even more than blue, we see the sky as blue because:
- Our eyes are more sensitive to blue light than violet
- The sun emits more blue light than violet
- Some violet light is absorbed by the upper atmosphere
Sky Without Atmosphere
If Earth had no atmosphere:
- The sky would appear black even during daytime
- Stars would be visible during the day
- No scattering would occur
- This is what astronauts see in space!
Why the sun appears red at horizon
The Red Sun Phenomenon
During sunrise and sunset, the sun appears reddish because sunlight travels through more atmosphere:
- Light travels through thicker layer of atmosphere
- Most blue light gets scattered away
- Only red and orange light reaches our eyes
- The sun appears 2 minutes before actual sunrise (advance sunrise)
- The sun remains visible 2 minutes after actual sunset (delayed sunset)
Move the slider to see how the sun's color changes throughout the day
How we use knowledge of light scattering in everyday life
π΄ Why Red for Danger Signals?
Red light is used for danger signals because:
- Red light has the longest wavelength in visible spectrum
- It scatters the least through fog, smoke, and dust
- Can be seen clearly from far distances
- Maintains its color even in poor visibility
Other Applications
βοΈ Aviation Lights
Aircraft use red lights on left wing, green on right for visibility and orientation
π Ocean Color
Deep ocean appears blue because water molecules scatter blue light while absorbing red
πΈ Photography
Golden hour photography utilizes warm colors during sunrise/sunset for dramatic effects
Quantitative relationship between wavelength and scattering intensity
Rayleigh Scattering Formula
I β 1/Ξ»β΄
Where I is the intensity of scattered light and Ξ» is the wavelength