Refraction of Light at Plane Surfaces Short notes and Selected PYQs

Refraction: The bending of light when it passes from one transparent medium to another due to change in speed.
Cause of Refraction: Light travels at different speeds in different media.
Normal: A line perpendicular to the surface at the point of incidence.
Angle of Incidence (i): Angle between incident ray and normal.
Angle of Refraction (r): Angle between refracted ray and normal.
Refraction towards/away from normal: Light bends towards normal when entering denser medium, away from normal when entering rarer medium.

First Law: The incident ray, refracted ray, and normal all lie in the same plane.
Second Law (Snell's Law): The ratio of sine of angle of incidence to sine of angle of refraction is constant for a given pair of media. sin i / sin r = constant.
Refractive Index (n): n = sin i / sin r = c/v, where c is speed of light in vacuum and v is speed in medium.
Absolute Refractive Index: Refractive index with respect to vacuum or air.
Relative Refractive Index: ₁n₂ = n₂/n₁ = v₁/v₂.

Definition: Measure of how much light slows down in a medium.
Formula: n = c/v = sin i / sin r.
Optical Density: Materials with higher refractive index are optically denser.
Examples: Refractive index of water ≈ 1.33, glass ≈ 1.5, diamond ≈ 2.42.
Relation: Higher refractive index means light travels slower in that medium.

Critical Angle: The angle of incidence in denser medium for which angle of refraction in rarer medium is 90°.
Total Internal Reflection (TIR): When light traveling from denser to rarer medium is completely reflected back at the interface.
Conditions for TIR: (1) Light must travel from denser to rarer medium. (2) Angle of incidence must be greater than critical angle.
Formula: sin C = 1/n, where C is critical angle and n is refractive index.
Applications: Optical fibers, prisms, mirages, diamonds' sparkle.

Real and Apparent Depth: Objects in water appear raised due to refraction. Apparent depth = Real depth / n.
Twinkling of Stars: Due to atmospheric refraction caused by varying density of air layers.
Mirage: Optical illusion caused by total internal reflection in hot air layers near ground.
Optical Fibers: Use TIR to transmit light signals over long distances for communication.
Principle of Reversibility: The path of light is reversible; incident and refracted rays can be interchanged.

Refraction of Light at Plane Surfaces