Ray Optics and Optical Instruments - Result Question 44

46. A convex lens of focal length 80cm and a concave lens of focal length 50cm are combined together. What will be their resulting power?

(a) +6.5D

(c) +7.5D

(b) 6.5D

(d) 0.75D

[1996]

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Answer:

Correct Answer: 46. (d)

Solution:

(d) We know that 1f=i=1n1fi

1f=1f1+1f2;f1=80cm,f2=50cm

1f=180100150100

P=1f=1.252=0.75D



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