## The Human Eye

The above applet models the eye.  The slider can be used to simulate the eye's ability to accommodate.  When the eye is in a relaxed state the focal length of the lens system of the eye is taken to be one.  Notice that as the eye accommodates to focus on nearby objects the focal length of the eye decreases.

The location of the near source can be changed by dragging the source.  The focal length of the eyeglass can be altered by clicking on eyeglass and then dragging the hotspots.

a) Is the eye represented in the above applet normal, nearsighted or farsighted? (click on the initialize link to start the applet)

b) If the eye is nearsighted, what power eyeglasses should be used for normal vision (can see far away objects with eyes relaxed, and also focus on an object at x=2.0)?

If the eye is farsighted, what power eyeglasses should be used to allow the person to see an object at x=2.0?  Would a farsighted person with these glasses still be able to focus on a far away object?  Why are farsighted individuals often prescribed bi-focals?

Physlet problem by Melissa Dancy and Wolfgang Christian.