Biomedical Engineering Reference
In-Depth Information
+20.00 D
C
F
′
-5.00 cm
-10.00 cm
Figure 14-6.
A mirror with a radius of curvature of
−
10.00 cm has a secondary focal
length of
−
5.00 cm and a power of
+
20.00 D.
Let us look at an example.
A concave mirror has a radius of curvature of 10.00 cm.
Where is the focal point located with respect to the mirror's surface? What is the
mirror's power?
As can be seen in Figure 14-6, the center of curvature of a concave mirror is
to the left of its surface. Using the linear sign convention that we have employed
throughout this topic (in which distances are measured from surfaces), this is desig-
nated as a negative distance. The focal length is calculated as follows:
r
=
2f
′
−
10.00 cm
=
2f
′
f
′
= −
5.00 cm
The focal point is located 5.00 cm to the left of the mirror's surface. The mirror's
power is
−
1
f
=
F
′
−
1
=
F
−
0.05 m
=
F
+
20.00 D
