Optics

Step 1: Understand the phenomenon of scattering of light.
Scattering of light is the process by which small particles (like air molecules, dust, water droplets) in the atmosphere deflect light from its straight path.
The amount of scattering depends on the wavelength of light and the size of the scattering particles.
Rayleigh scattering, which applies to particles much smaller than the wavelength of light (like air molecules), is more effective for shorter wavelengths (blue/violet light) than for longer wavelengths (red/orange light).
Specifically, scattering intensity .

Step 2: Explain the color of the sun at sunrise and sunset.
During sunrise and sunset, sunlight has to travel a longer path through the Earth's atmosphere to reach an observer compared to when the sun is overhead (noon).
- As sunlight passes through this longer atmospheric path, most of the shorter wavelength light (blue, violet) is scattered away from the direct line of sight by air molecules.
- The longer wavelength light (red, orange, yellow) is scattered less and therefore passes through the atmosphere more directly to the observer.
This results in the sun appearing reddish or orange, and the sky around the sun also taking on these hues.

Step 3: Evaluate the options.
Option (1) Scattering of Red light is very small: This is TRUE.
Red light, having a longer wavelength, is scattered much less by air molecules than blue light.
Because other colors are scattered away, red light is what predominantly reaches the observer from the sun.
Option (2) Scattering of Red light is very high: This is FALSE.
Red light is scattered the least among visible colors by air molecules.
Option (3) Sky is blue in colour: This is also due to Rayleigh scattering (blue light scattered more in all directions from sunlight), but it explains why the sky is blue during the day, not directly why the sun appears red at sunrise/sunset, although the same principle is at play.
Option (4) Muscles in the eye are not working properly: This is irrelevant to the atmospheric phenomenon.

Step 4: Identify the most direct reason.
The most direct reason is that red light is scattered the least, so it persists along the direct path from the sun to the observer when sunlight travels through a large amount of atmosphere.
Option (1) correctly states that the scattering of red light is very small.
This matches option (1).

Step 1: Understand the phenomenon described.
When sunlight passes through the canopy of a dense forest, the tiny water droplets or dust particles suspended in the air (mist/haze within the forest) scatter the sunlight, making the path of light visible.

Step 2: Relate this to known optical effects.
- Scattering effect: This is a general term for the deflection of light by particles.
Rayleigh scattering (by particles much smaller than wavelength, like air molecules) causes the blue sky.
Mie scattering (by larger particles) is less wavelength-dependent.
- Dispersion effect: The splitting of white light into its constituent colors (spectrum) when it passes through a prism or a medium where the refractive index varies with wavelength.
Not the primary effect here.
- Tyndall effect: This is the scattering of a beam of light by particles in a colloid or a very fine suspension.
The individual suspension particles scatter and reflect light, making the beam visible.
The path of light through a colloidal solution is visible from the side.
This accurately describes what happens when sunlight passes through mist or dust in a forest canopy.
- Colloid effect: This is not a standard specific optical term; "Tyndall effect" is the specific effect observed in colloids and fine suspensions.

Step 3: Identify the most appropriate term.
The visibility of light beams passing through the forest canopy due to scattering by suspended particles (like mist or dust, which can form a colloidal dispersion in air) is a classic example of the Tyndall effect.
This matches option (3).