Refraction of Light

Refraction is the change in direction and velocity of light as it passes from one medium to another of different optical density. This occurs because the speed of light varies across different media.

1. Laws of Refraction

• First Law: The incident ray, the refracted ray, and the normal at the point of incidence all lie in the same plane.
• Second Law (Snell's Law): The ratio of the sine of the angle of incidence (i) to the sine of the angle of refraction (r) is constant for a given pair of media. Mathematically: n = sin i / sin r.

2. Refractive Index (n)

The refractive index is a measure of how much light slows down in a medium. It is defined as:

• n = Velocity of light in vacuum (c) / Velocity of light in medium (v)
• n = Real Depth / Apparent Depth
• n = 1 / sin C (where C is the critical angle)

3. Total Internal Reflection (TIR)

TIR occurs when light travels from an optically denser medium to a less dense medium and the angle of incidence is greater than the critical angle. Critical Angle is the angle of incidence for which the angle of refraction is 90 degrees. Applications include:

• Optical Fibers: For high-speed data transmission.
• Mirages: Optical illusions caused by atmospheric refraction.
• Prism Binoculars and Periscopes.

4. Refraction through Glass Prisms

When light passes through a prism, it undergoes deviation. The angle of minimum deviation (D) is related to the refractive index (n) and the refracting angle (A) of the prism by the formula: n = sin[(A + D)/2] / sin(A/2).

5. Thin Lenses

Lenses are classified into two types:

• Convex (Converging): Thicker at the center, brings parallel rays to a focus.
• Concave (Diverging): Thinner at the center, spreads parallel rays out.

Lens Formulas

• Lens Formula: 1/f = 1/u + 1/v (where f is focal length, u is object distance, and v is image distance).
• Magnification (m): m = image height / object height = v / u.
• Newton's Formula: f² = ab (where a and b are distances of object and image from the focal points).