1

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)

C f

L O S T

C f

L O S T

C f

L O S T

Name (printed) _______________________________

2

C f

L O S T

R S O T

C f

L O S T

C f

L O S T

3

C f

L O S T

C f

L O S T

C f

L O S T

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List two similarities you see between your drawing and this photograph (taken by Ryan Warner, Class of 2010). 1. 2.

List two similarities you see between your drawing and this photograph (taken by Alison Haroff, Class of 2006). 1. 2.

List two similarities you see between your drawing and this photograph (taken by Alex Bond-Bishop, Class of 2010). 1. 2.

4

LAB REFLECTION FROM A CURVED MIRROR

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

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.

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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5

REFLECTION FROM A CURVED MIRROR (CONTINUED)

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: 1f =

1do+ 1

di. That’s the mirror equation, where

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

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 express the mirror equation as: f = dodi

do+di. 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.

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.”

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.

Figure 2: Real Image projected on card

di

do

6

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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7

PROCEDURE (PART 3)

1. 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.

2. 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: (behind mirror, between mirror and f, between f and C, at C, beyond C) Image orientation: (upright or inverted) Image size: (larger, smaller, or same) Image type: (real or virtual)

Object

Position 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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8

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)

Type of Mirror (Plane, Concave, Convex, or None)

Reason for choice

25.0 16.7

30.0 30.0

5.0 -10.0

15.0 -15.0

20.0 -5.0

40.0 -80.0

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9

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.