Chapter 10: Light Reflection and Refraction

Introduction

• Visibility depends on light reflection.
• Light travels in straight lines and forms rays.
• Common phenomena include image formation by mirrors, star twinkling, rainbows, and light bending.

Nature of Light

• Straight-line optics fails with diffraction, where light bends.
• Light exhibits wave and particle nature, explained by quantum theory.

Reflection of Light

Laws of Reflection

• Angle of incidence equals angle of reflection.
• Incident ray, normal, and reflected ray lie in the same plane.

Image by Plane Mirror

• Virtual, erect, equal in size, laterally inverted.

Curved Mirrors

• Concave Mirror: Curved inward, reflects inward.
• Convex Mirror: Curved outward, reflects outward.

Spherical Mirrors

• Pole (P): Center of reflecting surface.
• Centre of Curvature (C): Center of the sphere part.
• Radius of Curvature (R): Distance from pole to center.
• Principal Axis: Line through P and C.

Image Formation by Spherical Mirrors

• Concave Mirror: Various positions yield real or virtual images, varying in size.
• Convex Mirror: Produces diminished virtual images.

Mirror Formula

• Relationship: ( \frac{1}{v} + \frac{1}{u} = \frac{1}{f} )
• Magnification: ( m = \frac{h'}{h} = \frac{v}{u} )

Refraction of Light

• Light changes direction when entering a new medium.
• Apparent Depth: Objects appear shifted.

Laws of Refraction

• Snell's Law: ( \frac{\sin i}{\sin r} = \text{constant} )

Refractive Index

• Ratio of light speed in vacuum to medium.
• Higher refractive index = more optical density.

Lenses

Types of Lenses

• Convex Lens: Converges light, thicker in middle.
• Concave Lens: Diverges light, thicker at edges.

Image Formation by Lenses

• Convex Lens: Forms real or virtual images, enlarged or reduced.
• Concave Lens: Always forms diminished virtual images.

Lens Formula

• Relationship: ( \frac{1}{v} - \frac{1}{u} = \frac{1}{f} )
• Magnification: ( m = \frac{v}{u} )

Power of a Lens

• Definition: Reciprocal of focal length.
• Unit: Dioptre (D)
• Positive for convex, negative for concave.

Applications

• Concave Mirrors: Used in torches, headlights.
• Convex Mirrors: Rear-view mirrors due to wider field of view.
• Lenses: Used in glasses, cameras, microscopes.

Exercises

1. Material for lenses.
2. Virtual image by concave mirror.
3. Object position for real image by convex lens.
4. Image in a convex mirror.
5. Uses of different mirrors.
6. Nature of images formed by different lenses.
7. Calculation and application of mirror and lens formulas.