Question

An object is placed 20.0 cm from a convex mirror along the axis of the mirror. If a virtual image forms at a distance of 8.00 cm from the mirror, what is the focal length of themirror? Hint Watch Signs!

Answer 1

In order to determine the focal length of the given lens. Use the following formula:

`(1)/(f)=(1)/(s_o)+(1)/(s_i)`

where,

f: focal length = ?

so: object distance related to lens = 20.0 cm

si: image distance related to lens = -8.00 cm

Where the sign of si is '-' due to the image formed by the lens is virtual.

Then, by replacing, we obtain:

1/f = 1/20.0 - 1/8.00 = (8.00 - 20.0)/(20.0)(8.0) = -12.0/160.0 = -3/40

Then, the focal length is:

f = -40/3 cm ≈ -13.33cm

Hence, the focal length of the lens is approximately -13.33cm