Download concave mirror

Open up this document on the computer. Copy the data tables
into Excel. When you are done, copy your data table and graph
from Excel and paste them into this document. Then type your
responses to the discussion questions. Delete everything in red,
type your name, your lab partners’ names, and the date. Print the
entire resulting document and hand in.
Lab: Reflection in Curved Mirrors
PreLab Activity
Type your responses to these questions.
1. Look at your face in a small concave mirror.
a. Keeping the mirror vertical and close to your face, note what your image looks like.
b. Predict what will happen if you move the mirror further from your face.
c. Observe your image with your arm extended and record your findings.
2. Look at your face in a small convex mirror.
a. Keeping the mirror vertical and close to your face, note what your image looks like.
b. Predict what will happen if you move the mirror further from your face.
c. Observe your image with your arm extended and record your findings.
Objectives: Where is the focal point of a concave mirror? Where is the focal point of a convex mirror?
What are the characteristics of images produced by a concave mirror when the object moves from
beyond the center of curvature all the way to the focal point?
Hypotheses:
 The focal point of a concave mirror is located ________________________.
 The focal point of a convex mirror is located ________________________.
 As the object moves closer to the mirror, the size of the image becomes ______________________.
 As the object moves closer to the mirror, the orientation of the image ______________________.
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Materials: Optical Bench, Light source, circular reflecting surface, protractor, straight edge, compass,
pencil, black tape, white and/or tracing paper, mounted concave/convex mirrors, mounted
half screen.
PART A Procedure
1. Rotate the dial on the ray box so that five parallel rays are produced.
2. Put the data sheet on the table. Set up the light source on top of it, so that there are 5 individual
rays of light projected in the space, with the middle ray on the solid line in the box.
3. Put the concave mirror in front of the rays, adjusting it until you can see the convergence of the
reflected rays meet somewhere on the solid line. Trace the reflected rays on the paper, by making
a couple of dots and connect them with a ruler after removing the mirror.
4. The point of convergence is the focal point. Measure the focal length of the concave reflector.
Record it in the Data Table as fconcave.
5. Turn the reflector and repeat using the convex mirror. Trace the reflected rays on the paper, by
making a couple of dots and connect them with a ruler after removing the mirror.
6. Extend the rays back through the mirror, using a dashed line, until they meet at a point. The
distance to the convergence is the focal point. Measure the focal length and record it in the Data
Table as fdiv.
Observations and Analysis
Enter your data into the GoogleDoc. Record the class average when everyone is done. Then calculate the
percentage difference between your values and those of your classmates. Show your work for this.
Data Table 1: Focal Lengths
fconcave (cm)
Your Results
Class Average
% difference
f convex (cm)
PART B: Finding the relationship between object and image distance
7. Go to one station. The light source is secured at the 0 mm mark. The picture on the light source is
the object. Measure the size of the vertical arrow with a ruler and record it as the object size.
8. Record the focal length of the mirror (it should be printed underneath the mirror).
9. Record the location of the mounted mirror from the light source.
10. The half screen is located 10 cm from the light source. Move it until you get a focused image on the
screen. Measure and record the image distance and size of the image. Remember that inverted
images have negative heights. Return the screen to the 10 cm mark when you are done.
11. Rotate around to the remaining stations. Note that there may be some trials that produce no
image; therefore, “none” may be a valid observation.
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Data Table 2:
Station
Data and Observations for image distance and size
Focal Length
faverage (mm)
Object
Distance
(mm)
Object
Size
(mm)
Image Distance
(mm)
Image
Size
(mm)
1
2
3
4
5
6
7
PART C: Finding the focal length
12. The focal length of this concave mirror can be found by finding the location of an object that is
very far away from the mirror. The optics bench is pointing outside, towards the window, with the
mirror at the 0 mark. Move the half screen until you find the focused image of the building
opposite ours. Record the position from the mirror to the half screen.
13. Enter your data into the GoogleDoc. Record the class average when everyone is done. Then
calculate the percentage difference between your values and those of your classmates. Show your
work for this.
Data Table 3: Focal Length using an object distance of “infinity”
fstationC (cm)
Your Results
Class Average
% difference
Graph
In Excel, create a graph of the image distance (y-axis) versus the object distance (x-axis).
Paste the graph here when you are done.
Analysis Questions
1. How do your results compare to the class results for the focal lengths? Be specific here.
2. How do concave and convex mirrors reflect light differently?
3. Where is the focal point located for the concave mirror? For the convex mirror?
4. How well did your image characteristics agree with the predicted descriptions for Part B?
5. Real images are able to project onto a screen. The images you saw in a flat mirror are not real
images because they cannot be projected on a screen or card. Such images are called virtual
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images. Here,virtual means "not real." A virtual image seems to be a source of light rays but, in
reality, the light rays do not actually converge at a virtual image location.
a. Which stations produced real images?
b. Which stations produced virtual images?
6. At all stations where images were viewed, were the images formed by the mirror upright or
inverted?
7. What is the relationship between image distance and the object distance, as shown on your graph?
8. How did the image height change as the object was brought closer to the mirror?
Before you print this document, proofread for spelling. Be sure you have deleted all
type that is in RED, including these sentences. Insert page breaks to keep sections
on the same page. Especially make sure that you do not split tables onto multiple
pages. Attach the mirror diagrams!
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Light box
CONCAVE MIRROR
Light box
CONVEX MIRROR
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