Question

What is the focal length of the eye-lens system when viewing an object at infinity? Assume that the lens-retina distance is 2.0 cm . Follow the sign conventions. Express your answer using two significant figures and include the appropriate units.

Answer 1

Focal length of the eye-lens is 2.0 cm

Step-by-step explanation:

Given:

An eye-lens system which will follow converging lens (convex lens) sign conventions and knowing that lens-retina distance is the image distance.

Object distance,
`u` =
`-\infty`

Image distance,
`v` =
`2.0` cm

We have to find the focal length.

Lets say that the focal length is
`f` .

Lens Formula:

⇒
`(1)/(f) =(1)/(-u) +(1)/(v)`

Sign-convention:

We will follow the Cartesian coordinate,placing the lens at the origin of the plane, optical center is at
`(0,0)` now as the object will be towards negative x-axis so it is negative others are on the right side of the origin so they are positive.

Using the lens formula:

⇒
`(1)/(f) =(1)/(-u) +(1)/(v)`

⇒
`(1)/(f) =(1)/(-\infty) +(1)/(2.0)`

⇒
`(1)/(f) =0+(1)/(2.0)` ...as
`(1)/(\infty)=0` and there is no
`-0` so it is zero only.

⇒
`f=2.0` cm

So the focal length is 2.0 cm with two significant figures.