Question

A convex lens held some distance abovea 6 cm long pencil produces its imageof SOME size. On shifting the lens by adistance equal to its focal length, it againproduces the image of the SAME size asearlier. Determine the image size.​

Answer 1

Answer:

2cm.

Explanation:

Since, from the question we get that after shifting the lense so the magnification will be.

f/f+u   = - f/f+u+f

Hence, after solving for f we will get that f = (-2/3 )u.

Since, 1/f = 1/v – 1/u on which after substituting the value of  f we will get that v will be v = u/3.

Since, the formulae of the magnification for the original convex lense is = v/u hence it will be (u/3)/u.  

So, M = 1/3

Since, the object distance is given in the question as 6 cm.

So, 1/3 = v/6

Which on solving we will get v = 2 cm.