A convex lens is used to throw on a screen `10 m` from the lens, a magnified image of an object. If the magnification is to be `19`, find the focal length of the lens.

Answer

`0.5 m`

Explanation

Here, `v = 10 m, m = - 19, f = ?`
`m = (f - v)/(f)`
`-19 = (f - 10)/(f)` or `-19 f = f - 10` or `20 f = 10`
`f = 0.5 m`