๐Ÿ‘️ Introduction

This chapter explains the structure and working of the human eye and various phenomena related to light such as refraction through a prism, dispersion, scattering, and atmospheric effects.

๐Ÿ‘€ 1. Structure of the Human Eye

The human eye acts like a camera and helps us see the world around us.

๐Ÿ”น Parts of the Eye:

  • Cornea: Transparent front part that refracts light.

  • Iris: Colored part controlling the size of the pupil.

  • Pupil: Opening through which light enters.

  • Lens: Convex lens that focuses light on the retina.

  • Retina: Light-sensitive layer where image forms.

  • Ciliary Muscles: Change the shape of the lens to focus.

  • Optic Nerve: Carries visual information to the brain.

๐Ÿ”น Image Formation:

  • Light enters through the pupil.

  • Lens focuses light on retina.

  • Image is real and inverted.

  • Brain interprets the image as upright.

๐Ÿ”„ 2. Accommodation of the Eye

The ability of the eye lens to adjust its focal length to focus on near and distant objects is called accommodation.

  • For distant objects: Lens becomes thin.

  • For nearby objects: Lens becomes thick.

๐Ÿ”น Limits of Accommodation:

  • Near Point: 25 cm (minimum distance to see clearly)

  • Far Point: Infinity

๐Ÿ‘“ 3. Common Defects of Vision

  1. Myopia (Short-sightedness):

    • Can see nearby objects clearly

    • Distant objects appear blurred

    • Caused by elongated eyeball or lens too curved

    • Corrected by concave lens

  2. Hypermetropia (Long-sightedness):

    • Can see distant objects clearly

    • Nearby objects appear blurred

    • Caused by short eyeball or lens too flat

    • Corrected by convex lens

  3. Presbyopia:

    • Occurs with aging

    • Eye loses flexibility to focus

    • Corrected by bifocal lenses

  4. Cataract:

    • Clouding of the eye lens

    • Treated by surgery and lens replacement

๐Ÿ”บ 4. Refraction through Prism

A prism bends light due to refraction. The emergent ray bends away from the base.

  • Angle of deviation: Angle between incident and emergent ray

๐ŸŒˆ 5. Dispersion of Light

Dispersion: Splitting of white light into its 7 component colors (VIBGYOR).

  • Discovered by Isaac Newton

  • Occurs due to different refractive indices for different colors

๐ŸŒ† 6. Atmospheric Refraction and Scattering

๐Ÿ”น Atmospheric Refraction:

  • Refraction of light due to varying air density in atmosphere

  • Effects:

    • Star appears twinkling

    • Sun appears earlier at sunrise and later at sunset

๐Ÿ”น Scattering of Light:

  • Redirection of light by particles in the atmosphere

  • Tyndall Effect: Scattering of light by colloidal particles

๐Ÿ”น Applications:

  • Sky appears blue due to scattering of blue light

  • Sun appears reddish at sunrise and sunset due to longer path and scattering of shorter wavelengths

✅ Key Points to Remember

  • Eye can focus due to lens flexibility (accommodation)

  • Myopia and hypermetropia are corrected using lenses

  • Prism shows dispersion of light into spectrum

  • Atmospheric phenomena explained by refraction and scattering