Question

Use the mirror equation to show that an object placed between `f and 2f` of a concave mirror forms an image beyond `2f`.

Answer 1

Let `u = - (3f)/(2)` ,
When object lies between `f and 2 f`
From mirror equation
`(1)/(v)+(1)/(u)=(1)/(f)`
`(1)/(v)=(1)/(f)-(1)/(u)=(-1)/(f) + (2)/(3 f) = (-3 + 2)/(3 f) = -(1)/(3f)`
For concave mirror, `f` is neg.
`v = -3 f`
i.e., distance of image from the concave mirror is `3 f`, i.e., image formed is beyond `2 f`.