Light - PDF

Objectives: To study about reflection, refraction and dispersion of light. Ch.15 LIGHT What is Light? Light is the part of the Electromagnetic spectrum which we can see. Light travels in straight lines called rays (rectilinear propagation). A bundle of rays is known as a b...

Objectives: To study about reflection, refraction and dispersion of light. Ch.15 LIGHT What is Light? Light is the part of the Electromagnetic spectrum which we can see. Light travels in straight lines called rays (rectilinear propagation). A bundle of rays is known as a beam of light. A ray A parallel A A beam divergent convergent beam beam Luminous objects are which emit light by their own. Examples: - Sun, flame of a burning candle. Non-luminous objects are which can not emit light on their own. These objects reflect light from luminous bodies. Examples: - Moon, Earth. Pinhole Camera A pinhole camera is the simplest form of camera. The device doesn't have a lens. Instead, it is a light-proof box that has a small hole or aperture. This helps the camera to focus light on the light- sensitive material. The image formed is real and inverted. Transverse waves - oscillation of particles (or fields) is at right angles to the direction of energy transfer. They can travel in vacuum. Eg. Light wave Longitudinal waves - oscillation of particles is parallel to the direction of energy transfer. They can not travel in vacuum. Eg Sound wave Reflection Reflection is the bouncing of light rays off a surface. We are able to see non-luminous objects as light is reflected off them. Reflection Laws of Reflection The incident ray, the reflected ray and the normal all lie on the same plane. The angle of incidence is equal to the angle of reflection. i=r Reflection for Different Surfaces Regular reflection : On smooth surfaces with image formation. Diffused reflection :On rough surfaces without image formation. Properties of Image Formed by Plane Mirror Same size as the object Laterally inverted (left-to-right inversion) Upright Virtual (image cannot be caught on a screen) Object distance is equal to image distance Ray Diagram for Reflection Object, O observer Ray Diagram for Reflection Object, O Image, I observer Ray Diagram (Extended object) observer Refraction Refraction is the bending of light when it enters from one transparent medium into another. It is caused by the different speeds of light in different media. The greater the optical density of the medium, the slower the speed of light. Refraction Incident Angle of ray incidence Angle of refraction Refracted ray Angle of emergence Emergent ray normal Daily Phenomena of Refraction Swimming pool and ponds appear shallower than it really is. Object is at a deeper depth than where it appears to be. Bent objects in liquids. Total internal reflection: The situation when light has nowhere to refract and so reflects. Critical angle : Angle between the ray and the surface of a medium at which there is a change from refraction to total internal reflection. Dispersion of white light Dispersion of monochromatic light (single colour)