Question

A glass sphere of radius 10cm is kept inside water .A object o is placed front of shere.the position of o when seen from other side of the sphere is(refractive index of glass and water are1.5 and 1.33....)

Answer 1

1. A glass sphere of radius R = 10 cm is kept inside water. A point O is placed at 20 cm from A as shown in figure. find the position and nature of the image when seen from other side of the sphere. given µg = 3/L and µw = 4⁄3. 


Solution: A ray of light starting from O gets refracted twice. The ray of light is travelling in a direction from left to right. Hence, the distance meausred in this direction are taken + ve. 
Applying   ,   twice with proper signs.
we have,     or    AI1= - 30 cm 
Now, the first image I, acts as an object for the second surface, where 
   BI1 = u = - (30 + 20) = - 50 cm 

   
 BI2 = 100 cm, i.e. the final image I2 is virtual andis formed at a distance 100 cm (towards left) from B. 

Diagram 


2. Focal length of a convex lens in air is 10 cm. find its focal length in water. (µg = 3⁄2 ; µw = 4⁄3) 

Solution:    ………………………………………. (i) 
                ……………………………………. (ii) 
dividing equation (i) by (ii), we get 
       
=> fwater = 4 fair = 4 x 10 
             = 40 cm