Question

there is a spherical glass shell of refractive index 1.5 inner radius 10cm and outer radius 20cm. inside the spherical cavity there is air. a point objectis placed at a point O at a distance of 30cm

Answer 1

Answer:

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 

Explanation: