Reflection of Light
Reflection is the bouncing back of light rays when they hit a polished surface, like a mirror. The Laws of Reflection state that: (1) The angle of incidence is equal to the angle of reflection (∠i = ∠r). (2) The incident ray, the reflected ray, and the normal to the mirror at the point of incidence all lie in the same plane. A plane mirror always forms a virtual, erect, laterally inverted image of the same size as the object.
Spherical Mirrors
Spherical mirrors are part of a hollow sphere. There are two types:
- Concave Mirror: The reflecting surface curves inward. It converges light rays and can form both real (inverted) and virtual (erect) images depending on the object's distance. They are used in vehicle headlights, searchlights, and by dentists to see larger images of teeth.
- Convex Mirror: The reflecting surface curves outward. It diverges light rays and always forms virtual, erect, and diminished (smaller) images. They are primarily used as rear-view mirrors in vehicles because they provide a wider field of view.
Mirror Formula: 1/f = 1/v + 1/u, where f is the focal length, v is the image distance, and u is the object distance. Magnification (m) = -v/u.
Refraction of Light
Refraction is the bending of light when it passes obliquely from one transparent medium to another, caused by the change in the speed of light. When light travels from a rarer to a denser medium (e.g., air to glass), it bends towards the normal. When traveling from a denser to a rarer medium, it bends away from the normal.
Laws of Refraction (Snell's Law): The ratio of sine of the angle of incidence to the sine of the angle of refraction is a constant, known as the Refractive Index (n). n = sin(i) / sin(r). The refractive index is also the ratio of the speed of light in a vacuum to the speed of light in the medium (n = c/v).
Spherical Lenses
A lens is a transparent material bound by two surfaces. A Convex Lens is thicker at the center and converges light rays. A Concave Lens is thinner at the center and diverges light rays.
Lens Formula: 1/f = 1/v - 1/u. Magnification (m) = v/u.
Power of a Lens: The degree of convergence or divergence of light rays achieved by a lens is its power (P = 1/f, where f is in meters). The SI unit of power is Dioptre (D). A convex lens has positive power, while a concave lens has negative power.