Q5 of 50 Page 43

A power of convex lens is + 4.0 D. At what distance should the object from the lens be placed to obtain its real and inverted image of the same size on the screen?

Given;

Power of convex lens = + 4 D.


We know that;


Power (P) =


∴ Focal length (f) =


Hence f = 0.25 m.


Also


Given that;


Size of the object = size of the image.


For convex lens this is possible only when the object is placed at the centre of curvature.


∴ Object distance = 2f = 2 × 0.25 = 0.5 m.


0.5m = 0.5 × 100 = 50 cm.


Hence object is placed at 50 cm at centre of curvature.


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