Name (printed) _______________________________
ACTIVITY
MIRROR RAY DIAGRAMS
PROCEDURE
In the drawings on this and the following pages, the arrows represent objects in front of either concave or
convex mirrors.
• Make ray diagrams to locate the corresponding images. Draw in the complete image as an arrow.
• For each image arrow, indicate the:
- Location of the image, L (behind mirror, between f and C, at C, beyond C)
- Orientation of the image arrow, compared to the object arrow, O (upright or inverted)
- Relative size of image compared to the object arrow, S (smaller, same, larger)
- Type, T (real or virtual)
L
O
S
T
C
f
C
f
L
O
S
T
L
O
S
T
C
f
1
L
O
S
T
C
f
L
O
S
T
C
f
L
O
S
T
C
f
2
L
O
S
T
C
f
List two similarities you see
between your drawing and
this photograph (taken by
Alex Bond-Bishop, Class of
2010).
1.
2.
L
O
S
T
C
f
List two similarities you see
between your drawing and this
photograph (taken by Alison
Haroff, Class of 2006).
1.
2.
L
O
S
T
C
f
List two similarities you see
between your drawing and
this photograph (taken by
Ryan Warner, Class of
2010).
1.
2.
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GET CHECKED BEFORE MOVING ON
LAB
REFLECTION FROM A CURVED MIRROR
by a curved mirror can be closer to, farther away, or
even the same distance from the mirror as the object.
The image can be larger, smaller, or the same size. It
can be the same orientation as the object or inverted.
Finally, curved mirror images can be either real or
virtual. So with all these options, it might seem
impossible to look at curved mirror images with any
sense of order and simplicity. However, it turns out
that with concave mirrors there are only four
different styles of images. The style changes when
the object moves from region to region in front of the
mirror. The most important goal of this lab is to
discover these four styles and understand what the
rationale for the regions that they occur in.
INTRODUCTION TO PART 1
Images produced by mirrors can be defined
according to their style. Style refers to four particular
qualities of the image: its distance from the mirror
(compared to the object), its size (compared to the
object), its orientation (compared to the object), and
its type (real or a virtual image). Plane mirror images
are simplistic – they always have the same style.
Wherever you put the object, the image is always the
same distance behind the mirror as the object is in
front, always the same size as the object, always
upright, and always virtual.
Curved mirrors (concave or convex) produce
images with much more variety. The image produced
PROCEDURE (PART 1)
1.
Place the light bulb on the table so that all parts of the filament are the same distance from the reflecting portion
of the mirror (these are front-surface mirrors, so please don’t touch the reflecting surface). Then use a 3 x 5 card
to catch the image. This can be a bit difficult at first and takes a bit of practice. (It can also be impossible.
Remember, if the image being produced is virtual, it cannot be projected onto the card and will instead be
behind the mirror.)
2.
Practice moving the light bulb closer to and farther from the mirror until you get good at predicting what the
image will do. When you feel like you’ve got the hang of this, complete the statements below.
When comparing size use “smaller,” larger,” or “same size.”
When comparing orientation use “upright” or “inverted.”
a. When the image has a greater distance from the mirror than the object (light bulb filament), the image size is
____________________ than the object and its orientation is ____________________.
b. When the image has a smaller distance from the mirror than the object, the image size is
____________________ than the object and its orientation is ____________________.
c. When the image has the same distance from the mirror as the object, the image size is
____________________ than the object and its orientation is ____________________.
3.
There is a pattern between the image distance and the image size (compared to the object). What is that pattern?
4.
So far, all the images you’ve produced are real images (you were able to project them onto the card). Now get
the object very close to the mirror. You’ll produce a virtual image that you will need to look into the mirror to
see. Looking at the image, you should be able to see two fundamental differences between this virtual image
and the real images you produced earlier. What are these two differences?
•
•
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GET CHECKED BEFORE MOVING ON
REFLECTION FROM A CURVED MIRROR (CONTINUED)
between the focal length of a mirror, the distance an
object is placed in front of that mirror, and the
position where the image will form. If the object is
moved, the equation will specify where the new
image position will be. You can use algebra to
INTRODUCTION TO PARTS 2 AND 3
If you don’t like math, it’s probably because you
learned it in a math class. The problem with learning
math in a math class is that it’s typically taught and
learned out of context. Take calculus, for example.
Many of you are taking that class this year. You’ll
learn lots of rules and methods and techniques. But
calculus had one purpose when it was invented. Isaac
Newton developed calculus because he needed it to
understand the physics of gravity. That’s it!
Math is a language, much like the languages you
might be learning in the World Language
Department. Nature speaks … math. She will
communicate with you and even give up her ways
and her secrets, but only through math. So don’t be a
math-hater. We won’t be using super-sophisticated
math in this class and when we use math, it will
never be for math’s sake. Instead, we will use math to
communicate with nature.
So let’s see how that works. We’ll start with this:
1
1
1 . That’s the mirror equation, where
f = d +d
o
express the mirror equation as:
f = ddoo+ddi i .
In this
form, it is easy to measure an object distance and an
image distance and then calculate what the focal
length must be. That’s the next goal of the lab –
determine the focal length of your mirror. As you did
in Part 1, you’ll use the same light bulb filament and
3 x 5 card as your object and image.
A final goal of the lab is to link what you did in
Part 1 with what you do in Part 2. As mentioned
before, there are four different styles of images that
can be produced by a concave mirror. The style
changes when the object moves from region to region
in front of the mirror. The object regions are:
1. Between the mirror and the focus, “f.”
2. Between the focus and the center of
curvature, “C.”
3. At “C.”
4. Beyond “C.”
Your job is to establish the style of image
produced when the object is within each of these
regions.
i
f is the focal length
do is the distance an object is from the mirror
di is the distance the image is from the mirror
What nature is saying with this mathematical
equation is that there is a specific relationship
PURPOSE
To become familiar with the nature of the images formed by a concave mirror. Specifically, you will discover:
1. How to determine the focal length of a curved mirror
2. What the style of the image is (position, type, orientation, and relative size) when the object is in the following
positions: between the mirror and the focus, “f,” between the focus and the center of curvature, “C,” at “C,” and
beyond “C.”
di
do
Figure 1: Set up for collecting real image data. Be
careful to make measurements to the filament of the
light bulb, rather than the glass part of the bulb.
5
Figure 2: Real Image projected
on card
PROCEDURE (PART 2)
1.
Tape down a piece of white ticker tape approximately 1.5 meters long.
2.
Place the mirror at one end on a piece of clay.
3.
Direct the reflecting portion of the mirror directly down the ticker tape. Make a mark on the tape to indicate
where the reflective surface of the mirror is. (These are front-surface mirrors.)
4.
Place the light bulb on the table so that all parts of the filament are the same distance from the mirror. Then use
a 3 x 5 card to catch the image (see Figures 1 and 2). You can mark the object and image positions directly on
the tape and then measure them later. Do this for at least three object positions (one where the object is closer
to the mirror than the image, one where it is farther from the mirror than the image, and one where the object
and image are at the same location).
5.
Make a neat data table below. Use a straightedge and label the columns carefully. Record the object and image
distances as well as the calculated focal length. If the precision of your focal length calculations is poor, keep
taking data until it improves. It is reasonable to throw out obvious outliers before you calculate the average
focal length.
DATA AND CALCULATIONS
6.
Calculate the average focal length and center of curvature.
Average focal length, f = ______________
Center of curvature, C = ______________
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GET CHECKED BEFORE MOVING ON
PROCEDURE (PART 3)
1.
2.
Turn your ticker tape over so that there are no markings on it. Mark the tape again where the surface of the
mirror will be. Measure out from the mirror position and mark where the focal length and the center of
curvature are.
Now use your light bulb to test the style of the image produced by a curved mirror for each of the object
positions indicated (with the exception of the region between the mirror and the focus). For the object position
between the mirror and the focus, use a pencil as the object and peer into the mirror, comparing the image of the
pencil to the actual pencil. Use the table below to describe the image.
The possible entries for the table are shown in parentheses below.
Image location:
Image orientation:
Image size:
Image type:
Object
Position
(behind mirror, between mirror and f, between f and C, at C, beyond C)
(upright or inverted)
(larger, smaller, or same)
(real or virtual)
Concave Mirror Images
Position
Size
Orientation
Type
Mirror F
F C
C
Beyond C
3.
State how the image size changes when the object moves within (not between) each of the following positions:
a. From the mirror to the focus.
b. From the focus to the center of curvature.
c. Beyond the center of curvature.
4.
The tables below are like the one that appears above. These are for the much simpler plane and convex mirrors
(which each only have one style of image). Use what you know about or observe in these kinds mirrors to fill in
the tables using the same descriptors as you used in the table above.
Object
Position
Plane Mirror Images
Position
Size
Orientation
Type
Anywhere
Object
Position
Convex Mirror Images
Position
Size
Orientation
Type
Anywhere
Use the tables you created on the previous page to answer the next questions.
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GET CHECKED BEFORE MOVING ON
For credit, you must provide a clear and complete explanation for each of the questions below.
5. _____ The distance of an object from a concave mirror is varied until both object and image distances are 100
cm from the mirror. What is the focal length of the mirror?
a. 50 cm
b 100 cm
c. 150 cm
d. 200 cm
6. _____ A concave mirror has a center of curvature of 20 cm. For which object distance will the image be real,
inverted and larger than the object?
a. 5 cm
b. 10 cm
c. 15 cm
d. 28 cm
7. _____ The distance of an object from a concave mirror is varied until both object and image distances are 50 cm
from the mirror. How does the size of the image compare to the size of the object when the object is
moved out to 65 cm from the mirror?
a. smaller than the object
b. same size as the object
c. larger than the object
8. _____ If you wanted to use the mirror in the previous question to help you to apply makeup, where would you
place your face in order to use it as it is intended to be used (that is, upright and magnified)?
a. less than 25 cm
b. 25 cm – 50 cm
c. 50 cm
d. > 50 cm
9. _____ You pull the bowl of a spoon closer and closer to your eye and notice that the image of your eye flips
right side up when the spoon is 2.0 cm away. How far would you put a candle flame away from the
spoon if you wanted to make the largest possible image of the flame out in front of the spoon on a wall?
a. less than, but very close to 2.0 cm
c. less than, but very close to 4.0 cm
b. greater than, but very close to 2.0 cm
d. greater than, but very close to 4.0 cm
10. The table below lists object and image distances for objects in front of six different mirrors. Identify each type
of mirror?
Object
Distance (cm)
Image
Distance (cm)
25.0
16.7
30.0
30.0
5.0
-10.0
15.0
-15.0
20.0
-5.0
40.0
-80.0
Type of Mirror (Plane,
Concave, Convex, or None)
Reason for choice
GET CHECKED BEFORE MOVING ON
8
MIRROR EQUATION PROBLEM SOLVING
In the space below, do the following problems from the hardcover book:
Regular Physics: Page 659, problems 9, 10, 11, 12
Honors Physics: Page 659, problems 10, 12, 14, 20, 22
Start each problem with givens (like I taught you) and show all work.
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