Human eye

• Vitamin A is necessary for good vision and can be found in raw carrots, broccoli, green vegetables, cod-liver oil, etc.
• To protect your eyes, remember to:

  • Avoid reading in dim light
  • Wash your eyes at least four times a day with clean and cold water
  • Wash your eyes quickly if dust particles or small insects enter your eye
  • Visit an eye specialist regularly to prevent stress, eyestrain, and headaches
  • Maintain a distance of at least 25 cm between your eyes and the book while reading
  • Avoid rubbing your eyes and consult an eye specialist if redness persists
  • Avoid direct exposure to sunlight to prevent harm to the retina
• Power of accommodation:

  • Ability of the lens to adjust its focal length
  • Thickness of the lens is controlled by ciliary muscles
  • Nearest focal distance of lens is 25 cm
• Defects in vision:

  • Myopia/near-sightedness:
  • Problem: Distant objects cannot be seen clearly
  • Image is formed in front of the retina
  • Correction: concave lens
  • Hypermetropia/far-sightedness:
  • Problem: Near objects are not seen clearly
  • Image formed beyond the retina
  • Correction: convex lens
  • Presbyopia:
  • Near-focus distance increases with age
  • Power of accommodation decreases
  • Correction: Bi-focal lens and concave lens
• Refraction through a prism:

  • Light bends due to refraction at points B and C
  • Angle of deviation is the extent of deviation of the light ray from its path BE to path CD
• Dispersion of light:

  • White light splits into seven constituent colors when passing through a glass prism
  • Red disperses least, violet disperses most, yellow is the average of all lights
• Formation of rainbow:

  • Natural phenomenon where white sunlight splits into beautiful colors by water droplets
• Flickering of objects:

  • Air above the fire is relatively hotter than the air further up in the atmosphere
• Twinkling of stars:

  • Caused by changing air density in the atmosphere
• Early sunrise and delayed sunset:

  • Caused by refraction of light through the atmosphere
• The sun and planets do not twinkle because they are not seen as point sources like stars, but are considered as extended sources
• Scattering of light:

  • Phenomenon of absorption and re-emission of light
  • Scattering of light by colloidal particles gives rise to the Tyndall effect
  • Atmospheric particles, smoke, tiny water droplets, suspended dust particles, and air molecules scatter sunlight, making the path of light visible
• Sky is blue because light near the blue wavelength scatters the most
• Danger signs are red in color because red light scatters the least