Light Reflection and Refraction

Introduction

• Light is a form of energy that travels in a straight line.
• This chapter focuses on the reflection and refraction of light.

Reflection of Light

• Definition: When a light ray strikes a smooth, polished surface like a mirror, it bounces back.
• Mirrors: Opaque objects with shiny, reflective surfaces allow us to see our images due to light reflection.

Types of Mirrors

1. Plane Mirrors

   • Create virtual images located behind the mirror.
   • Images are the same size as the object and are laterally reversed.

2. Spherical Mirrors

   • Convex Mirrors: Outward-curved reflective surfaces.
   • Concave Mirrors: Inward-curved reflective surfaces.

Key Terms for Spherical Mirrors

• Pole (P): Center point of the reflecting surface.
• Center of Curvature (C): Center of the imaginary sphere from which the mirror is derived.
• Radius of Curvature (R): Radius of the imaginary sphere.
• Principal Axis: Line joining the pole and center of curvature.
• Principal Focus (F): Point where light rays parallel to the principal axis converge.
• Focal Length (f): Distance between the pole and the principal focus.

Image Formation by Mirrors

• Concave Mirrors: Varying positions of objects lead to different image characteristics.
• Convex Mirrors: Produce erect, diminished virtual images, typically used as rearview mirrors.

Refraction of Light

• Definition: Change in direction of light when it passes from one medium to another, caused by a change in speed.
• Observations such as a bent straw in a glass are due to refraction.

Laws of Refraction

1. Incident ray, refracted ray, and normal lie in the same plane.
2. Ratio of sine of angle of incidence to sine of angle of refraction is constant (Snell's Law).

Refractive Index

• Measure of how much light speed is reduced in a medium compared to a vacuum.
• Different materials have different refractive indices (e.g., water ~1.33, diamond ~2.42).

Spherical Lenses

• Types: Convex (converging lenses) and Concave (diverging lenses).
• Principal Focus (F): Focal point where light rays converge or appear to diverge.

Rules for Ray Diagrams in Lenses

• Rays parallel to the principal axis pass through or appear from the principal focus.
• Rays passing through the optical center emerge undeviated.

Image Formation by Lenses

• Convex Lenses: Real and inverted images, varying with object position.
• Concave Lenses: Virtual and erect images, typically diminished.

Sign Conventions and Formulas

• Mirror Formula: ( \frac{1}{v} + \frac{1}{u} = \frac{1}{f} )
• Lens Formula: ( \frac{1}{v} - \frac{1}{u} = \frac{1}{f} )
• Magnification: Ratio of image height to object height, can also be expressed as ( \frac{-v}{u} ) for mirrors.

Power of Lenses

• Definition: Measure of a lens's ability to bend light, denoted by ( P = \frac{1}{f} ) (in diopters).
• Positive Power: Converging lens (Convex).
• Negative Power: Diverging lens (Concave).

This completes the discussion on the reflection and refraction of light.