🌟 Chapter 10: The Human Eye and the Colourful World

🎯 Class 10 Science Notes (Easy + Exam Oriented)

👁️ 1. The Human Eye

• Eye is a natural optical instrument to see objects.
  
  

• Parts of Eye:
  
  

  • Cornea: Transparent layer that refracts light.
    
    

  • Iris: Controls size of pupil.
    
    

  • Pupil: Controls amount of light entering the eye.
    
    

  • Lens: Convex lens that focuses light on retina.
    
    

  • Retina: Screen with photoreceptors.
    
    

  • Ciliary muscles: Adjust lens shape.
    
    

👉 Hindi: Aankh ek prakritik yantra hai jo chhavi banata hai retina par.

👀 2. Accommodation of Eye

Ability of eye lens to adjust its focal length to focus nearby or distant objects.

👉 Hindi: Aankh ka apne lens ki focal length ko badalna jisse door aur paas ki vastu saaf dikhe.

📏 3. Near Point and Far Point

• Near Point: 25 cm
  
  

• Far Point: Infinity
  
  

• Range of Vision: 25 cm to ∞
  
  

😵 4. Defects of Vision and Corrections

Defect

Cause

Correction

Myopia (Nearsightedness)

Lens too curved / Eyeball too long

Concave lens (-)

Hypermetropia (Farsightedness)

Lens too flat / Eyeball too short

Convex lens (+)

Presbyopia

Ageing – ciliary muscles weak

Bifocal lens

👉 Hindi: Nazar ke defects ko alag-alag lenses se theek kiya ja sakta hai.

🌈 5. Dispersion of Light

Splitting of white light into 7 colours (VIBGYOR) by a prism.

👉 Hindi: Jab prism se safed roshni gujarti hai to 7 rangon mein toot jaati hai.

🧪 6. Cause of Dispersion

Different colours of light bend at different angles due to different wavelengths.

🔄 7. Recombination of Colours

When second prism is used upside down, it combines the spectrum to form white light again.

🌦️ 8. Rainbow Formation

• Sunlight enters raindrops (dispersion, reflection, refraction)
  
  

• Light splits and comes out in form of rainbow
  👉 Hindi: Rain ke drops prism ki tarah kaam karte hain.
  
  

🌌 9. Atmospheric Refraction

Light bends due to varying densities in the atmosphere.

Examples:

• Twinkling of stars
  
  

• Sun appears earlier and sets later
  
  

• Sun appears flat during sunrise/sunset
  
  

👉 Hindi: Vayu mandal mein prakash ka modna refraction ke karan hota hai.

📘 Important Questions – With Answers

✅ 1 Mark Questions

1. What is the near point of a normal human eye?
   👉 25 cm
   
   

2. Which lens is used to correct myopia?
   👉 Concave lens
   
   

3. Name the phenomenon due to which stars appear to twinkle.
   👉 Atmospheric refraction
   
   

✅ 2 Mark Questions

1. What is meant by dispersion of light?
   👉 Splitting of white light into its 7 colours by a prism.
   
   

2. Why does the sun appear red during sunrise and sunset?
   👉 Because red light scatters the least and reaches our eyes.
   
   

✅ 3 Mark Questions

1. State the cause of twinkling of stars.
   👉 Due to atmospheric refraction; light path keeps changing due to temperature variations.
   
   

2. Explain the formation of rainbow.
   👉 Due to dispersion, total internal reflection and refraction inside raindrops.
   
   

3. Differentiate between myopia and hypermetropia.
   
   

Myopia

Hypermetropia

Cannot see far objects

Cannot see near objects

Concave lens is used

Convex lens is used

✅ 5 Mark Questions

1. Explain the working of human eye with a neat diagram.
   👉 Draw eye diagram, label all parts, explain each (cornea, iris, pupil, lens, retina etc.)
   
   

2. What is atmospheric refraction? Explain any two natural phenomena due to it.
   👉 Bending of light in atmosphere.
   Examples:
   
   

• Twinkling of stars
  
  

• Early sunrise and late sunset