The distance of an object from the principal focus of a concave mirror of focal length F is D. The ratio of the size of image to the size of object is
a) F/D
b) (F/D)2
c) (F/D)1/2
d) F+D/F-D

Dear Student ,
Here in this case the object distance , u = D and the focal length is f = F .
Now let us take that the image distance is v .
So applying the equation of spherical mirror we get ,
1v+1u=1f1v+1D=1F1v=1F-1D=D-FFDv=FDD-FNow as we know that the magnification is , m=Image distanceObject distance=Image sizeObject sizeSo , vu=Image sizeObject sizeObject sizeImage size=FDD-FD=FDD(D-F)=F(D-F)

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