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348
CHAPTER 25
25.22
(a) The lateral magnification produced by the objective lens of a good compound
microscope is closely approximated by
1
O
ML
f
≈ −
, where
L
is the length of the
microscope tube and
is the focal length of this lens. Thus, if
and
O
f
20.0 cm
L
=
1
50.0
M
=−
(inverted image), the focal length of the objective lens is
1
20.0
0.400 cm
50
= +
−
cm
.0
O
L
f
M
≈−
(b) When the compound microscope is adjusted for most comfortable viewing (with
parallel rays entering the relaxed eye), the angular magnification produced by the
eyepiece lens is
25 cm
ee
mf
=
. If
20.0
e
m
=
, the focal length of the eyepiece is
25.0 cm
25.0 cm
1.25
20.0
e
e
f
m
===
cm
+
(c) The overall magnification is
()
(
)
1
50.0
20.0
1000
e
mMm
==
−
=
−
25.23
The overall magnification is
11
25 cm
e
e
mMm M
f
where
1
M
is the magnification produced by the objective lens. Therefore, the required
focal length for the eye piece is
( )( )
1
12
25 cm
25 cm
2.1 cm
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This document was uploaded on 10/20/2011.
 Spring '09
 Physics, Work

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