Nguyen, Thanh – Homework 21 – Due: Apr 22 2008, 7:00 pm – Inst: Weathers
1
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printout
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have
14
questions.
Multiplechoice questions may continue on
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before answering.
The due time is Central
time.
001
(part 1 of 2) 10 points
An object is
p
= 44
.
6 cm in front of a concave
mirror. Its real image height is 7 times larger
than the object height.
p
h
What is the location of the image?
Correct answer: 312
.
2 cm.
Explanation:
1
p
+
1
q
=
1
f
=
2
R
m
=
h
0
h
=

q
p
Concave Mirror
f >
0
∞
> p > f
f < q <
∞
0
> m >
∞
f > p >
0
∞
< q <
0
∞
> m >
1
Let :
M
=

7
and
p
= 44
.
6 cm
.
Let the location of the image be denoted as
q
.
q
p
h
h'
f
R
Since the image is 7 times larger than the
object, and is a real image, as stated in the
problem (
p >
0 and
q >
0), the magnification
must be negative;
i.e.
,
M
=

7.
M
=
h
0
h
=

q
p
=

7
,
so
q
=

M p
=

(

7) (44
.
6 cm) =
312
.
2 cm
.
002
(part 2 of 2) 10 points
What is the radius of curvature of the mirror?
Correct answer: 78
.
05 cm.
Explanation:
Now that we have
q
and
p
, we can find the
radius of the curvature via the relationship
1
p
+
1
q
=
2
R
or
R
=
2
p q
p
+
q
=
2 (44
.
6 cm) (312
.
2 cm)
44
.
6 cm + 312
.
2 cm
=
78
.
05 cm
.
keywords:
003
(part 1 of 2) 10 points
A concave spherical mirror has a radius of
curvature of 34
.
6 cm
.
The object distance is
9
.
1 cm
.
h
0
q
h
p
f
R
Scale: 10 cm =
Find the magnitude of the image distance.
Correct answer: 19
.
1988 cm.
Explanation:
1
p
+
1
q
=
1
f
=
2
R
M
=
h
0
h
=

q
p
Concave Mirror
f >
0
f > p >
0
∞
< q <
0
∞
> M >
1
Note:
The radius of curvature for a concave
mirror is positive,
R
= 34
.
6 cm.
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Nguyen, Thanh – Homework 21 – Due: Apr 22 2008, 7:00 pm – Inst: Weathers
2
Solution:
Substituting these values into the
mirror equation
q
=
1
1
f

1
p
=
1
2
R

1
p
=
1
2
34
.
6 cm

1
9
.
1 cm
=

19
.
1988 cm

q

=
19
.
1988 cm
.
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