5.2 Understanding refraction of light

~Refraction of light is a phenomenon where the direction of light is changed when it crosses the boundary between two materials of different optical densities.
~Refraction of light occurs as a result of a change in the velocity of light as it passes from one medium into another medium.                   
                                             
*Angle of incidence,i is the angle between the incident ray and the normal.
*Angle of refraction,r is the angle between the refracted ray and the normal.

Laws of Refraction 
~the incident ray,the refracted ray and the normal to the interface are all lie in the same plane.
~the value of sin i /sin r is constant.
~is known as snell' law. 


Refraction index and the Speed of Light  
~amount of bending depends on the ratio of speed of light in a vacuum to the speed of light in the medium.
~this ratio is called the refractive index of the medium.
           
                 n = speed of light in vacuum /speed of light in the medium
                    = c / v        


Substance       Refractive index
Air                          1.00
Vacuum                  1.00
Water                     1.33
Ice                          1.31
Glass                      1.50
Perspex                  1.49
Diamond                 2.40

Apparent Depth and Actual Depth
(a) Apparent Depth ,d
     The distance of the image from the surface of the water 
(b) Actual Depth
     The distance of the object from the surface of the water 
                      Refractive index,n = Real depth,D / Apparent depth,d

(a) a man standing in a boat and observes an object in the sea.

(b) ray of light from the object travel from water to air.

(c)water is denser than water.

(d) rays of light refract away from the normal as they leave the water .

(e) the rays of light enter the eyes of the observer.

(f) the observer see a virtual image above the object.

(g) so the object appears to be nearer the surface of the water. 

(a) water is denser than air.

(b) when the light rays emerge from the surface of the water,they are refracted away from the normal.

(c) the emergent light rays appear to originate from the position of the virtual image.

(d) the light rays from all the points along the length of the pen immersed in the water are similarly refracted.

(e) the submerged portion of the pen appears to the above of object.

(f) so giving the impression that the pen is bent.