An object is kept at a distance of `16 cm` from a thin lens and the image formed is real. If the object is kept at a distance of `6 cm` from the lens, the image formed is virtual. If the sizes of the images formed are equal, the focal length of the lens will be

Answer

11 cm

Explanation

For real image m = `(-f)/(f+16)`
Virtual `m= (f)/(f+6)`
`therefore (-f)/(f+16) = (f)/(f+16) implies f+16 = -f-6`
`2f = -22 implies f = 11 cm`