Refraction of light (class 10) science

REFRACTION OF LIGHT

CLASS 10

SCIENCE 

IMPORTANT POINTS

Refraction Of Light

The phenomenon of change in path of light when it passes from one medium to another is called Refraction.

Cause of Refraction

The bending of light takes place when it passes from one medium to another because speed of light changes from one medium to another.Speed of light is different in different media.

Laws of Refraction

The incident ray, the refracted ray, and the normal at the point of incidence are all contained within a single plane.

Refraction Through A Rectangular Glass Slab

When light passes through a rectangular glass slab, it undergoes refraction at both the entry and exit faces:

Entry Refraction: As light enters the glass from air, it bends towards the normal due to the slower speed of light in the denser glass.

Inside the Slab: The light travels in a straight line within the slab, still refracted but at an angle to the normal.

Exit Refraction: Upon leaving the slab, the light bends away from the normal as it moves back into the less dense air.

Key Points

Parallel Faces: The entry and exit rays are parallel because the angle of incidence equals the angle of emergence.

Lateral Displacement: Although parallel, the light is displaced sideways from its original path, depending on the slab's thickness, the angle of incidence, and the glass's refractive index.

In essence, while the light rays remain parallel, they shift from their initial path due to refraction

Refractive Index

Refractive index of a medium

 

The relative refractive index of a medium 2 w.r.t medium 1 is the ratio of speed of light in medium 1 to the speed of light in medium 2.

 

 

 Absolute Refractive Index of a Medium

The proportion of speed of light in vacuum to the speed of light in a material is called absolute refractive index of medium.

 Optically denser-Greater the value of n less will be the speed of light.

Optically rarer-Lesser the value of n greater will be the speed of light

Image Formation In Spherical Lenses

(A). Rules to obtain images in Convex lens

1. A ray parallel to the principal axis moves through the focal point after refraction.

 2. A ray passing through the focal point emerges parallel to the principal axis.

3.  A ray through the optical center continues straight without deviation.

Sign Convention For Spherical Lenses

Lens Formula And Magnification

The relationship between object distance(u) ,image distance(v) and the focal length(f) is given by 

 

 Magnification-The ratio of height of image 

  to the height of object .

Power Of Lens

It is the extent of convergence or divergence of light rays. Falling on it.A lens of short focal length bends the light rays more through large angles.

The power of a lens is defined as the inverse of its focal length. 

 Units is Dioptre (D)

For convex lens power is positive and for concave lens power is negative.