NEET Physics Ray Optics and Optical Instruments Questions Solved


The size of the image of an object, which is at infinity, as formed by a convex lens of focal length 30 cm is 2 cm. If a concave lens of focal length 20 cm is placed between the convex lens and the image at a distance of 26 cm from the convex lens, calculate the new size of the image

(a) 1.25 cm                              (b) 2.5 cm

(c) 1.05 cm                              (d) 2 cm

(b) Convex lens will form image at I1 it’s focus which acts like a virtual object for concave lens.

                    
Hence for concave lens u=+4 cmf=20 cm.

So by lens formula 1-20=1v-14v=5 cm i.e. distance of final image I2  from concave lens v=5 cm by using vu=IO54=I2I2=2.5 cm

Difficulty Level:

  • 24%
  • 45%
  • 18%
  • 15%
Crack NEET with Online Course - Free Trial (Offer Valid Till September 21, 2019)