The Human Eye and the Colourful World
1. The Human Eye
The human eye is a natural optical instrument used for vision. It functions similarly to a camera with a lens and screen system.
- Retina: Light-sensitive screen inside the eye where the image is formed, containing rods and cones.
- Cornea: Thin membrane covering the eyeball, refracts light entering the eye.
- Aqueous humour: Fluid filling the space between the cornea and eye lens.
- Eye lens: Convex lens made of flexible, transparent jelly-like material. Its curvature is adjustable via ciliary muscles.
- Pupil: Hole in the iris allowing light into the eye, appearing black due to light absorption.
- Ciliary muscles: Muscles attached to the eye lens that modify its shape to vary focal lengths.
- Iris: Controls light entry by adjusting the pupil size.
- Optical nerve: Transmits the image to the brain via electrical signals.
2. Accommodation Power
The ability of the eye to change the focal length of the lens using ciliary muscles to get a clear view of objects at various distances.
3. Colour Blindness
Some people lack cone cells responding to certain colours due to genetic disorders.
4. Myopia (Short-sightedness)
A condition where distant objects appear blurry, caused by excessive corneal curvature or elongated eyeball.
5. Hypermetropia (Long-sightedness)
A condition where near objects appear blurry, caused by a decrease in eye lens power or shortened eyeball.
6. Presbyopia
Age-related vision defect caused by reduced lens flexibility and weakening ciliary muscles.
7. Astigmatism
A condition where horizontal and vertical lines cannot be focused simultaneously.
8. Cataract
Membrane growth over the eye lens making it hazy or opaque, leading to vision loss. Corrected via surgery.
9. Dispersion of White Light by a Glass Prism
White light splits into seven colours (VIBGYOR) when passing through a glass prism, forming a spectrum.
10. Composition of White Light
White light consists of violet, indigo, blue, green, yellow, orange, and red.
11. Monochromatic Light
Light of a single colour or wavelength, e.g., sodium light.
12. Polychromatic Light
Light with multiple colours or wavelengths, e.g., white light.
13. Recombination of White Light
Newton demonstrated that an inverted prism can recombine dispersed light into white light.
14. Formation of a Rainbow
Water droplets act as prisms, refracting and dispersing sunlight internally before exiting, creating a rainbow.
15. Atmospheric Refraction
Refraction caused by air layers of varying optical densities.
16. Effect of Atmosphere on Day Duration
Due to atmospheric refraction, the Sun appears earlier at sunrise and later at sunset, extending the day by about 4 minutes.
17. Scattering of Light
According to Rayleigh’s law, shorter wavelengths like violet and blue scatter more, making the sky appear blue.
18. Colour of the Sun at Sunrise and Sunset
During noon, sunlight travels a shorter distance and appears white. At sunrise and sunset, shorter wavelengths scatter more, making the Sun appear red.