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Lehigh University
Physics 21, Spring 2008
April 2, 2008
HW24 Solutions
241.
(HRW 3443)
You produce an image of the Sun on a screen, using a thin lens
whose focal length is 20.0 cm. What is the diameter of the image? (See Appendix
C
for
needed data on the Sun.)
Solution:
43. Let the diameter of the Sun be
d
s
and that of the image be
d
i
. Then, Eq. 345 leads to
( )( )( )
28
3
11
2
0
.
01
0 m 2 6
.
9
61
0m


1.86 10 m
1.50 10 m
1.86mm.
is
s
s
if
dm
d
d
d
pp
−
−
××
⎛⎞
==
≈
=
=
×
⎜⎟
×
⎝⎠
=
242.
(HRW 3447)
An illuminated slide is held 44 cm from a screen. How far from the
slide must a lens of focal length 11 cm be placed (between the slide and the screen) to
form an image of the slide's picture on the screen?
Solution:
47. Using Eq. 349 and noting that
p + i = d
= 44 cm, we obtain
p
2
–
dp + df
= 0.
Therefore,
pd
d
d
f
=±−
=
±
−
=
1
2
4
22
44
4 44
22
2
()
(
(
cm
1
2
cm)
cm)(11 cm)
cm.
2
243.
(HRW 3491)
Someone with a near point P
n
of 25 cm views a thimble through a
simple magnifying lens of focal length 10 cm by placing the lens near his eye. What is the
angular magnification of the thimble if it is positioned so that its image appears at (a) P
n
and (b) infinity?
Solution:
91. (a) Without the magnifier,
θ
=
h
/
P
n
(see Fig. 3419). With the magnifier, letting
i = –
i = – P
n
, we obtain
11
11111
pfifi
fP
n
=−
=+=+
.
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This note was uploaded on 04/13/2008 for the course PHYSIC 2 taught by Professor Kim during the Spring '08 term at Lehigh University .
 Spring '08
 Kim
 Physics

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