posted by Kyle on .
Ordinary glasses are worn in front of the eye and usually 2.00 cm in front of the eyeball. A certain person can see distant objects well, but his near point is 60.0 cm from his eyes instead of the usual 25.0 cm. Suppose that this person needs ordinary glasses.
What focal length lenses are needed to correct his vision ?
Here's my work so far:
I think that since the near point is 60cm, the image should be at 60cm from the lens, but since the lens is worn 2cm from the eye, the focal length should be 60-2 so 58cm, right?
A converging or positive lens is required, with
a power such that when an object is placed 25 cm in front of the
lens, the lens forms a virtual image.
The image distance di= 60 cm, so that this image serves as an
object for the eye at the eye’s near point.
Taking into account the distance 2 cm
di =0.62 m, do =0.27m
Applying the thin lens equation, we ﬁnd
1/F =1/do +1/di = 1/0.27 +1/0.62 =3.7+1.61 =5.31.
F = 0.188 m