Convex lens has a focal length of 10cm a) where should the object be placed if the image is to be 30 cm from the lens on the same side as the object? (b) What will be the magnification?

Convex lens has a focal length of 10cm a) where should the object be p

1.	Convex lens has a focal length of 10cm a) where should the object be placed if the image is to be 30 cm from the lens on the same side as the object? (b) What will be the magnification?
Answer» Solution : In case of magnifying lens, the lens is convergent and the image is erect, ENLARGED, virtual, between infinity and object and on the same side of lens as shown in figure. So here f=10 cm and v=-30cm HENCE from lens -formula. `1/v-1/u=1/f` we have `1/(-30)-1/u=1/10` i.e., u=-7.5 cm So the object must be PLACED in front of lens at a distance of 7.5 cm (which is `LT f`) from it. (b) `m=[I/O]=v/u=(-30)/(-7.5)=4` i.e., image is erect, virtual and four times the size of object.