Question

PLEASE ANSWER THE QUESTIONS WITH EXPLANATION.

1 mm bug located at the near-point, 25 cm away from the left eye. Includes the distance between the retina and lens in your eye is 1 cm.

What focal length for your eye lens is needed to focus the bugs' image onto your retina?

If you insert a convex magnifying glass of 6 cm away from the bug, between the bug and your eye, How far away from the glass lens will the virtual image of the bug be located if the focal length of that glass lens is 7 cm?

Answer 1

Solution:

(a)

The bug is located at 25cm in fron the eye.

The distance between retina and eye lens is 1cm.

  

Let the focal length be f.

By lens formula,

  

  

(b)

Refraction through glass:

The focal length of the magnifying glass is 7cm. The glass is at 6cm from the bug.

,

By lens formula,

So after refraction through magnifying glass the first image will be at 42cm infront of the glass.

Refraction through eye lens:

The image formed by refraction through glass will be the object for the eye lens. The distance between glass and lens is 19cm. That image is at a distance of 19+42=61 cm from the eye lens.

  ,  

By lens formula,

  

  

The final image is at a distance of 0.97cm away from eye lens. So, it is at a distance of 0.97+19=19.97cm from the magnifying glass.