Question

a spherical mirror produces a magnification of -1 on a screen placed at a distance of 40cm from the mirror i) write the type of mirror ii) What is the focal length of the mirror

Answer 1

f =-20 cm

Step-by-step explanation:

Given that,

The magnification of a spherical mirror, m = -1

The image distance, v = 40 cm (for negative magnification)

The magnification of a concave mirror is negative. The mirror showing -1 magnification is a concave mirror.

Let f be the focal length of the mirror. We know that,

`m=(-v)/(u)\\\\-1=(-v)/(u)\\\\v=u`

Object distance, u = -40 cm

Using mirror's formula i.e.

`(1)/(f)=(1)/(u)+(1)/(v)\\\\f=(1)/((1)/(-40)+(1)/(-40))\\\\f=-20\ cm`

So, the focal length of the mirror is 20 cm.