Optics 3 Question 13

13. The image of an object, formed by a plano-convex lens at a distance of 8m behind the lens, is real and is one-third the size of the object. The wavelength of light inside the lens is 2/3 times the wavelength in free space. The radius of the curved surface of the lens is

(2013 Adv.)

(a) 1m

(b) 2m

(c) 3m

(d) 6m

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Answer:

Correct Answer: 13. (c)

Solution:

  1. μ=λair λmedium =1(2/3)=32

Further, |m|=13=|vu|

|v|=|u|3

u=24m

v=+8m

(Real object)

(Real image)

 Now, 1v1u=1f=(μ1)1+R118+124=3211RR=3m



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