Question

A concave mirror forms a real image at 20 cm from the mirror surface along the principal axis. If the corresponding object is at a 380cm distance, what is the mirror’s focal length?

Answer 1

Given that the image distance is v = -20cm

The object distance is u = -380 cm.

We have to find the focal length, f.

The formula to find the focal length is

`(1)/(f)=(1)/(u)+(1)/(v)`

Substituting the values, the focal length will be

`\begin{gathered} (1)/(f)=(1)/(-380)+(1)/(-20) \\ =-(1)/(19) \\ f=-19\text{ cm} \end{gathered}`

Thus, the focal length is -19 cm.