NEET Physics Ray Optics and Optical Instruments Questions Solved

NEET - 2016

 

Two identical glass μg=3/2 equi-convex lenses of focal length f each are kept in contact. The space between the two lenses is filled with water μw=4/3. The focal length of the combination is

(a)  f/3             (b) f

(c) 4f3               (d) 3f4

 

(d) consider the situation shown is figure. Let radius of curvature of lens surfaces is R. The combination is equivalent to three lenses in contact.

    1feq=1f1+1f2+1f3=2f1+1f2            f1=f3

                  

Now1f1=1f3=1f=μ-11R-1-R=μ-12RR=2fμ-1

      1f2=μw-1-1R-1R=μw-1-2R=43-1-2R      =13-2R=-2312fμ-1

1f2=-13132-11f          =-23×1f 1feq=2f-23×1f=6-23f=43ffeq=3f4

Difficulty Level:

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