Class 10 Science The Human Eye and the Colourful World

Class 10 Science The Human Eye and the Colourful World

Introduction

  • Human Eye: An organ responsible for vision, allowing us to perceive the world around us.
  • Colourful World: Refers to how light interacts with objects to create the colours we see.

1. Structure of the Human Eye

  • Cornea: Transparent layer that covers the eye, focuses light.
  • Pupil: Circular opening that controls the amount of light entering the eye.
  • Iris: Coloured part of the eye, adjusts the size of the pupil.
  • Lens: Focuses light onto the retina.
  • Retina: Light-sensitive layer that captures light and sends signals to the brain.
  • Optic Nerve: Carries electrical signals from the retina to the brain.

Near and Distant Vision

  • Ciliary muscles change the shape of the lens to focus on objects at different distances.
    • Accommodation: Ability of the eye to focus on both near and distant objects by changing the lens shape.

2. Defects of the Eye

  1. Myopia (Short-sightedness):
    • Can see near objects clearly, but distant objects are blurry.
    • Caused when the eyeball is too long or the lens is too curved.
    • Corrected using concave lenses.
  2. Hypermetropia (Long-sightedness):
    • Can see distant objects clearly, but near objects are blurry.
    • Caused when the eyeball is too short or the lens is too flat.
    • Corrected using convex lenses.
  3. Presbyopia:
    • Age-related condition where the ability to focus on near objects decreases.
    • Corrected using bifocal lenses.
  4. Astigmatism:
    • Caused by an uneven curvature of the cornea or lens, resulting in blurred vision.
    • Corrected with cylindrical lenses.

3. The Phenomenon of Light

  • Reflection: When light bounces off a surface.
  • Refraction: Bending of light when it passes through different mediums.
  • Dispersion: Separation of light into its constituent colours (like in a prism).
  • Scattering of Light: When light is scattered in all directions by particles. This causes the sky to appear blue and the sun to appear red at sunset.

4. Dispersion of Light and the Colour Spectrum

  • White light consists of seven colours: Violet, Indigo, Blue, Green, Yellow, Orange, Red (VIBGYOR).
  • Dispersion: When light passes through a prism, it is dispersed into its component colours.
  • Rainbow: Natural phenomenon caused by dispersion, reflection, and refraction of light in water droplets in the atmosphere.

5. Applications of Refraction and Dispersion of Light

  1. Spectacles: Convex lenses for hypermetropia and concave lenses for myopia.
  2. Cameras and Microscopes: Use of lenses for magnification and clear vision.
  3. Prism: Dispersion of light into a spectrum of colours.
  4. Rainbow: Occurs after rain due to dispersion and reflection of sunlight in water droplets.