## 14 May 2011

### LIGHT - REFLECTION AND REFRACTION Notes-2

Mirrors Formula
There is a relationship between the distance of image (v), distance of object (u) and the focallength of a spherical mirror (f) which is given by the Mirror Formula. The mirror formula is, 1/v =1/u +1/f
Magnification
The magnification of a spherical mirror gives the relative extent to which the image of an object is magnified with respect to the object size. It is expressed as the ratio of the height of image to the height of object.
m= hi/ ho = -v/u           M is –ve for inverted image and +ve for erect image.
Refraction : The phenomenon of bending of light as it travels from one medium to another medium . It is due to that velocity of light get changed in different medium . When light enters from a rarer medium into a denser medium it will bend towards the normal. Similarly when light gets into a rarer medium from a denser medium it will bend away fro the normal.
Laws of Refraction
There are two laws of refraction:
(i) The incident ray, the refracted ray and the normal to the interface of the two media at the point of incidence - all lie in the same plane.
(ii) The ratio of the sine of the angle of refraction for a given pair of media is constant. This is known as Snell’s Law.
Refractive Index
It is the ratio of the angle of incidence to the sine of the angle of refraction when light is refracted from one medium to another medium.
Spherical Lens A lens is a transparent material bound by two curved surfaces of which one or both surfaces are spherical, through which light can pass. There are two types of lenses: Concave Lens and Convex Lens.
Concave Lens A lens having two curved refracting  surfaces having thinner in the middle thicker to edge.
Convex Lens  A spherical lens having two curved refracting surfaces and thicker in middle and thinner to the edge.
Optical Center  It is the center inside the lens. A ray of the light passing through the optical center of a lens show no deviation.
Center of Curvature of a Lens
It is the center point of arcs of the two spherical surfaces  of the lens is made. Since a lens constitutes two spherical surfaces, it has two centers of curvature.
Radius of Curvature of a Lens is the distance between the optical center and the center of curvatures
Principal Axis of a Lens : It is an imaginary line passing through the two centers of curvature of a lens
Power of a Lens The power of a lens is defined as the reciprocal of its focal length.  P = 1/ f (m) Its SI unit is Dioprer( D)