Biomedical Engineering Reference
In-Depth Information
Sample Problem 1: Converging Surface
An object is located 50.00 cm to the left of a
5.00 D spherical crown glass
surface. How far is the image from the apex of the surface? Is the image real or
virtual? Is it erect or inverted? If the object is 3.00 cm in height, what is the height
of the image?
+
First, draw a diagram (Fig. 3-5). (Always draw a diagram!) The object vergence
at the refracting surface is
n
l
L
=
1.00
L
=
=
−
2.00 D
−
0.50 m
or
(100)(1.00)
−
L
=
=
−
2.00 D
50.00 cm
Light with a vergence of
−
2.00 D is incident upon a surface whose power is
+
5.00 D. What is the vergence of the light rays after they are refracted? According
- 50.00 cm
L
= -2.00 D
F
= +5.00 D
+3.00 cm
n
= 1.00
n
′
= 1.52
I
O
-1.98 cm
L
′
= +3.00 D
+ 50.67 cm
Figure 3-5.
Rays diverging from an object,
O
, are converged by the plus surface to
form a real image,
I
. The diagram shows rays emerging from the base of the object,
at the point where it intersects the optical axis. Object vergence and surface power
are given above the surface, and image vergence is given below the surface; we will
follow this convention throughout this topic.
This diagram and others in this chapter
are not drawn to scale
.
