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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

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

Grade:upto college level

2 Answers

Saurabh Koranglekar
askIITians Faculty 10335 Points
3 years ago
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Vikas TU
14149 Points
3 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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