Question

Playing with an old lens one morning, Ravi discovers that if he holds the lens 10cm away from a wall opposite to a window, he can see a sharp but upside -down picture of outside world on the wall. That evening, he covers a
lighted lamp with a piece of opaque paper on which he has pierced, a small hole 1 mm in diameter. by placing the lens between the illuminated card and the wall, he manages to produce a sharp image of diameter 5 mm on the wall. Answer the following questions based on the above information : (i)what is the power of the lens? (ii)in the evening experiment, how far away from the opaque paper did he place the lens? (iii)How far apart were the card and the wall?

Answer 1

Morning experiment:
   Since the objects are far away outside the window, u = - ∞. Hence a sharp image is formed inverted at the focus.  So f = 10 cm. Since inverted image is formed (real), it is a convex lens.

i)    Power of lens = 100/10 = 10 D

Evening experiment
    magnification = - 5 = v/u 
      v = -5u     => u = -v/5

   lens equation   1/v - 1/u = 1/f
                            1/v + 5/v = 1/10 
                             6/v = 1/10   =>   v = 60 cm
                             u = -v/5 = -12 cm
ii) 12 cm
iii)  12+60 = 72 cm

Answer 2

can you please tel me tha from which book this question paper is taken

Explanation:

please