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358
CHAPTER 25
(b) If the object distance must be
26.0 cm
p
=
to position the image at
, the
actual focal length is
75.0 cm
q
=−
()
( )
26.0 cm
75.0
m
26.0 cm
75.0
pq
f
pq
−
==
+−
cm
0.398
cm
=
and
11
2.51
0.398 m
f
=
+
P
(
diopters
The error in the power is
)
2.67
2.51 diopter
∆=
−
P
s
0.16 diop
=
ters too low
25.50
(a) If
q
=
when
, the thin lens equation gives the focal
length as
2.00 cm
1.00 m
100 cm
p
100 c
cm
100 cm
pq
f
m
2.00 cm
1.96
2.00 cm
=
++
(b) The
f
number of a lens aperture is the focal length of the lens divided by the
diameter of the aperture. Thus, the smallest
f
number occurs with the largest
diameter of the aperture. For the typical eyeball focused on objects 1.00 m away,
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This document was uploaded on 10/20/2011.
 Spring '09
 Physics, Power, Work

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