Reflection of Light

• Light is a form of energy that enables sight by bouncing off objects and being processed by our brains.
• Maxwell theorized light is electromagnetic radiation, with magnetic and electric fields traveling as waves at the speed of light.
• Light exhibits both wave and particle natures, depending on the circumstances, according to wave-particle duality in quantum mechanics.
• Diffraction, polarization, and interference are explained by considering light as a wave; the photoelectric effect is explained by considering light as particles called photons.

Reflection of Light

• Regular reflection occurs when light strikes a polished surface with minimal irregularities, like a plane mirror although the surface abosrbs some light.
• The incident ray, reflected ray, and normal all lie in the same plane.
• The angle of incidence equals the angle of reflection (∠i = ∠r).
• Fermat's Principle provides observations useful for understanding geometric optics.
• A mirage is an example, where hot air near the road reflects light, creating the illusion of water.

Plane and Spherical Mirrors

• A plane mirror is a flat, polished surface with few irregularities that reflects light.
• Light reverses its path upon reflection from a surface.
• Spherical mirrors are curved mirrors created from a slice of a hollow sphere.
• Focal length is half the distance between the pole and the radius of curvature in a spherical mirror.
• Ray diagrams are used to determine image formation for objects at various positions, especially with concave mirrors.
• Concave and convex mirrors have everyday uses like rear-view mirrors, lamps, and solar cookers.
• The mirror formula is 1/f = 1/v + 1/u, where 'u' is object distance, 'v' is image distance, and 'f' is focal length.
• In a coordinate system, distances measured towards positive x and y axes are positive, while those towards negative axes are negative, with the pole (P) as the origin.
• Object height is usually positive (above the principal axis), and image height is usually negative (below the principal axis).
• Magnification formula: m = h'/h = – (v/u); a negative m indicates a real image, and a positive m indicates a virtual image.

Refraction of Light

• Light bends when entering a different medium because it takes the quickest path, known as refraction.
• The relative refractive index is the refractive index of one medium with respect to another; with respect to a vacuum, it is the absolute refractive index.
• Light passing through a rectangular glass slab exits parallel to the incident ray but is laterally displaced.
• The refractive index measures the extent of light bending, depending on the ratio of speeds in the two media.
• Refractive index formula: n = sin∠i/sin∠r = (speed of light in medium 1)/(speed of light in medium 2).
• Relative refractive index formula: n = c/v, where n is the refractive index, c is the speed of light in a vacuum, and v is the speed of light in the medium.
• Laws of refraction apply when light passes through a curved surface, like lenses.
• Convex lenses bulge outward, while concave lenses curve inward.

Lenses

• Lens formula: 1/f = 1/v - 1/u, relates object distance (u), image distance (v), and focal length (f).
• Lenses are used in spectacles, binoculars, magnifying lenses, and telescopes.
• The power of a lens is the reciprocal of its focal length in meters (1/f).
• The SI unit of lens power is the dioptre (D).