a. From observation 3 image distance = object distance so radius of curvature = 40 cm
so focal length is half of the radius of curvature = 20 cm
b. Observation 6 is not correct as the object is placed between optical center and focus so the image will be erect and virtual, so image distance will not be positive.
u = -60 cm; v = + 30 cm f = - 20 cm
m = v/u = 30/-60
m = -0.5
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