Railway Science (Physics-Light and Optics) (Part-V)

Away from the normal. Refraction of light: When a ray of light passes from one medium to another, its velocity and direction change on entering the second medium, that is, the ray of light deviates from its path. Rarer medium is a medium in which the speed of light is more. Example: Air is optically rarer medium as compared to glass and water. Denser medium is a medium in which the speed of light is less. Example: Glass is optically denser medium as compared to air.

Optical Centre. Sign Convention for Spherical lens - The axis along which the distances are measured is called the principal axis. These distances are measured from the optical center of the lens. The distance measured above the principal axis is taken positive, distance below the principal axis is considered as Negative. Focal length of convex lens is taken positive and that of concave lens is negative.

Refractive index (n):- Measures the bending of a ray of light when passing from one medium into another. It is calculated as n = c / v, where c = speed of light in air and v = phase velocity of light. Refractive index of some material - Air (1.0003), Water (1.33), Diamond (2.42).

Focus F. Pole (P) - Center of the reflecting surface of a spherical mirror. Center of curvature (C) - Center of the sphere formed by the reflecting part of a spherical mirror. Radius of curvature (R) - Radius of the sphere of which the mirror forms the part. Principal axis - A straight line joining the pole (P) and the center of curvature. It is normal for the mirror at its pole. Principal focus - The incident rays coming parallel to the principal axis after reflection appear to converge to a common point on the principal axis. Focal length (f) - Distance between the pole and the principal focus of a spherical mirror.

Principal axis. Radius of Curvature - Distance between Centre of curvature and surface of lens. Focal Length -The distance of the principal focus from the optical centre of a lens. Aperture - The effective diameter of the circular outline of a spherical lens is called its aperture. Relation between Focal length and Radius of Curvature for
Lens: 1/f = (n - 1) (1/R1 - 1/R2). Where f - focal length, (R1, R2) - radius of curvature , n - refractive index of the material of the lens. It is also known as the lens maker's formula.

Light. Photolysis - Chemical process by which molecules are broken down into smaller units through the absorption of light. Example - photolysis of water during photosynthesis in plants. Other reactions affected by light: The photosynthetic production of starch by plants from carbon dioxide and water. photochemical reaction, a chemical reaction initiated by the absorption of energy in the form of light.

Centre of curvature C. In case of curved mirrors the normal passes through the center of curvature, and here the angle of incidence is 0°. That is, the ray passing through the center of curvature is incident normally to the mirror. The angle of reflection should also be 0°.

Violet (having the shortest wavelength and the highest frequency). The red light bends the least, with the longest wavelength (lowest frequency).

Isaac Newton. Dispersion of light - The process of the separation of white light into different colors when the light is passed through the prism. Other discoveries: Newton - Reflecting telescope, discovered calculus, three laws of motion, law of universal gravitation. Henry Cavendish - Discoverer of hydrogen. C V Raman - Discovered ‘The Raman Effect’. John Dalton - Proposed the ‘Modern Atomic Theory’.

Ice, Kerosene, Benzene, Rock salt. Refractive index - It is the ratio of the speed of light in a vacuum to that in a second medium of greater density. It depends on the Density of the medium and is dimensionless.