Question

A convex lens forms an image that of the same size that of the object ; when it is kept at 20cm in front of the lens. What will be the order of u , v and f for this condition

A)u= -20cm , v= +20cm , f= -20cm
B)u= -20cm , v=+20cm , f= -10cm
C)u= +20cm , v= -20cm , f= +10cm
D)u= -20cm , v= +20cm , f= +10cm

Answer 1

Answer:

u=-20 and image is on the other side of the lens, so v=+20, when the size of the image is equal to the size of the object, the object is kept at the centre of curvature, and for convex lens it is positive

so r=20, f=20/2=10

Ans is D