🔦 Chapter 2: Light – Reflection and Refraction (Class 10 Physics Notes)

 Welcome to the world of mirrors and lenses! In this chapter, you’ll understand how light behaves, how images are formed, and the rules behind reflection and refraction.

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🌟 What is Light?

Light is a form of energy that enables us to see objects. It travels in straight lines and can reflect, refract, or be absorbed.

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🔁 Reflection of Light

👉 Definition:

Reflection is the bouncing back of light from a shiny surface (like a mirror).

🔄 Laws of Reflection:

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

2. Angle of incidence = Angle of reflection

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🪞 Types of Reflection

Type	Description
Regular	From smooth surfaces, clear image
Irregular	From rough surfaces, blurred image

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🔍 Spherical Mirrors

Two types:

1. Concave (Converging)

2. Convex (Diverging)

Important Terms:

• Pole (P): Center of mirror

• Focus (F): Point where rays converge/diverge

• Center of curvature (C): Center of the sphere

• Principal axis: Line passing through P and C

• Focal length (f): Distance between P and F

🧠 F = R/2 (R = Radius of curvature)

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🪞 Mirror Formula:

$$\frac{1}{f} = \frac{1}{v} + \frac{1}{u}$$

• $f$ = focal length

• $v$ = image distance

• $u$ = object distance
  (Use sign conventions)

🔎 Magnification (m):

$$m = \frac{h_i}{h_o} = \frac{-v}{u}$$

Where $h_i$ = height of image, $h_o$ = height of object

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🌈 Refraction of Light

👉 Definition:

Refraction is the bending of light as it passes from one medium to another.

⚠️ It occurs due to change in speed of light.

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📘 Laws of Refraction:

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

2. Snell’s Law:

   $$\frac{\sin i}{\sin r} = \text{constant} = \mu$$

   Where $\mu$ = refractive index

🧠 Refractive Index:

$$\mu = \frac{\text{speed of light in vacuum}}{\text{speed in medium}}$$

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🔍 Lenses

Two types:

• Convex Lens (Converging)

• Concave Lens (Diverging)

Lens Formula:

$$\frac{1}{f} = \frac{1}{v} - \frac{1}{u}$$

🔎 Magnification for lens:

$$m = \frac{h_i}{h_o} = \frac{v}{u}$$

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📌 Uses of Mirrors and Lenses:

• Car headlights (concave mirror)

• Rearview mirror (convex mirror)

• Magnifying glass (convex lens)

• Peepholes (concave lens)

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💡 FAQs:

Q1: What happens when light passes from air to water?

It bends towards the normal because speed decreases.

Q2: What mirror is used in a dentist's tool?

Concave mirror to get magnified, upright image.

Q3: What type of lens is used in spectacles for myopia?

Concave lens