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Grade upto college level Engineering Entrance Exams

Two thin convex lenses of focal length 10 cm and 15 cm are combined together, the focal length of the combination is a) 25cm b) 12.5cm c) 15cm d) 6cm

Profile image of aditya kashyap
12 Years agoGrade upto college level
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2 Answers

Profile image of Saurabh Koranglekar
6 Years ago
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Profile image of Vikas TU
6 Years ago
The object distance is given, it is 40 cms away from the convex lens.
Now the light from the source will meet the convex mirror after getting refracted from the convex lens, and then light will retrace its path. To retrace its path, the light must fall on the convex mirror in such a way that the rays would meet it's centre of curvature if extended.
So radius of curvature =2f=2*7.5=15 cm
So object distance =-40 cm
     Image distance = d+15 cm

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