Question

solve question no. 4 plzz

Answer 1

Let the real depth of water be h.
So, h' = h-1   [ Microscope is raised upon 1 cm focus]
We know,
the formula of refractive index when,
the real depth and apparent depth is given to us.
So , n =    real depth     
              apparent depth
       n = h
             h'
 nh-n = h
      h =  n
            n-1 
Put the values:
h =    4
         3    
      4 - 1
      3   
h =  4
      3   
       1
       3
h = 4  × 3
      3      1
h = 4 cm

∴ Water pound into beaker = upto 4 cm
(4) option is correct... 4 cm

Answer 2

I am not sure but...hope it's right.

We are viewing at the coin through the  microscope from a direction/position vertically above the coin.

Let water be poured into the beaker to a height of h.  The real depth of the coin in h.  The apparent image of the coin forms at h' deep from the surface of water.  It means that h-h' is the lift or raise by which the image of coin is lifted.

The focus of the microscope is not changed. But only it is raised. So its point of focus is lifted /raised up by 1cm.  So microscope focuses on the virtual image formed by water.

Hence,  h - h' = 1 cm.

Now we know the formula :   h / h' = μ
              h = 4 h'/3
        So  4h'/3 - h' = 1 cm
                h ' = 3 cm
                h = 3+1 = 4 cm

Hence the height to which water should be poured is 4 cm.