🔥 Chapter 9: Light – Reflection and Refraction

🎯 Class 10 Science Best Notes (With Hindi Explanation)

🌟 1. What is Light?

Light is a form of energy that enables us to see things.
👉 Hindi: Light ek urja hai jo hume cheezein dekhne mein madad karti hai.

🪞 2. Reflection of Light

Bouncing back of light from a smooth surface like mirror.
👉 Hindi: Jab light kisi chamakdaar satah se takra kar wapas laut jaati hai.

📏 3. Laws of Reflection

1. Incident ray, reflected ray, and normal lie in the same plane.
   
   

2. Angle of incidence = Angle of reflection
   👉 Hindi: Aapaat aur pratibimban ka kona barabar hota hai.
   
   

🔍 4. Spherical Mirrors

🔹 Concave Mirror (Converging)
🔹 Convex Mirror (Diverging)
👉 Hindi: Concave andar ki taraf muda hota hai, convex bahar ki taraf.

📘 5. Image Formed by Concave Mirror

Position of Object

Position of Image

Nature

At infinity

At focus

Real, inverted, very small

Beyond C

Between F and C

Real, inverted, small

At C

At C

Real, inverted, same size

Between C and F

Beyond C

Real, inverted, large

At focus

At infinity

Real, inverted, very large

Between F and mirror

Behind mirror

Virtual, erect, enlarged

👉 Hindi: Concave mirror alag-alag jagah par vastu rakhne par alag prakar ke chhavi banata hai.

📘 6. Image Formed by Convex Mirror

Always virtual, erect and smaller in size
👉 Hindi: Convex mirror hamesha virtual aur chhoti chhavi banata hai.

🧮 7. Mirror Formula

1f=1v−1u\frac{1}{f} = \frac{1}{v} - \frac{1}{u}f1​=v1​−u1​

• f = focal length
  
  

• v = image distance
  
  

• u = object distance
  👉 Sign convention ka use karna hota hai.
  
  

💡 8. Refraction of Light

Bending of light when it passes from one medium to another.
👉 Hindi: Jab light ek madhyam se doosre mein jaati hai to uska rukh mud jaata hai.

📐 9. Laws of Refraction

1. Incident ray, refracted ray and normal lie in same plane.
   
   

2. Snell’s Law:
   
   

sin⁡isin⁡r=constant\frac{\sin i}{\sin r} = \text{constant}sinrsini​=constant

👉 Hindi: Snel ka niyam kehta hai sin i/sin r ek constant hota hai.

🧪 10. Refractive Index

n=cvn = \frac{c}{v}n=vc​

• c = speed of light in vacuum
  
  

• v = speed of light in medium
  👉 Hindi: Refractive index se pata chalta hai ki light kitni dheemi hui hai.
  
  

🔍 11. Lens and Its Types

🔹 Convex Lens (Converging)
🔹 Concave Lens (Diverging)
👉 Hindi: Convex lens light ko ek jagah jodta hai, concave lens failata hai.

📘 12. Image by Convex Lens

Position of Object

Position of Image

Nature

At infinity

At focus

Real, inverted, point size

Beyond 2F

Between F and 2F

Real, inverted, small

At 2F

At 2F

Real, inverted, same size

Between F and 2F

Beyond 2F

Real, inverted, large

At F

At infinity

Real, inverted, very large

Between F and optical center

Same side of lens

Virtual, erect, enlarged

📘 13. Image by Concave Lens

Always virtual, erect and smaller
👉 Hindi: Concave lens hamesha virtual aur chhoti chhavi banata hai.

🔍 14. Lens Formula

1f=1v−1u\frac{1}{f} = \frac{1}{v} - \frac{1}{u}f1​=v1​−u1​

👉 Same formula as mirror, bas lens ke sign convention use hote hain.

📘 Important Questions for Practice — With Answers

✅ 1 Mark Questions

1. What is the nature of image formed by convex mirror?
   👉 Virtual, erect and diminished
   
   

2. What is the mirror formula?
   👉 1f=1v−1u\frac{1}{f} = \frac{1}{v} - \frac{1}{u}f1​=v1​−u1​
   
   

3. Name the mirror used in vehicles as rear-view mirror.
   👉 Convex mirror
   
   

✅ 2 Mark Questions

1. State two differences between convex and concave mirror.
   | Convex Mirror | Concave Mirror | |---------------------|----------------------| | Diverges light | Converges light | | Always virtual image| Can form real image |
   
   

2. What is refractive index? Write its formula.
   👉 It shows how much a ray of light bends.
   Formula: n=cvn = \frac{c}{v}n=vc​
   
   

✅ 3 Mark Questions

1. Draw ray diagram for object between F and pole of concave mirror.
   👉 (Diagram required)
   Image formed is virtual, erect, and magnified.
   
   

2. Explain the laws of reflection.
   👉
   
   

• Incident ray, reflected ray and normal lie on same plane
  
  

• Angle of incidence = Angle of reflection
  
  

3. State sign convention for spherical mirrors.
   👉
   
   

• Distances measured in direction of light are positive
  
  

• Opposite direction: negative
  
  

• Distances above principal axis: positive
  
  

• Below principal axis: negative
  
  

✅ 5 Mark Questions

1. Draw ray diagrams for all image formations in concave mirror.
   👉 (6 positions – diagrams required)
   Describe each with position, size, and nature.
   
   

2. Explain refraction of light with laws and formula.
   👉 Refraction is bending of light at interface of two media.
   Laws:
   
   

• Incident ray, refracted ray, normal lie in same plane
  
  

• Snell’s Law: sin⁡isin⁡r=constant\frac{\sin i}{\sin r} = \text{constant}sinrsini​=constant
  Formula: n=cvn = \frac{c}{v}n=vc​