Activity: What is the relationship between the angle of incidence and
the angle of reflection? How is a virtual image formed? What is the
field of vision for a given location in front of a mirror?
Equipment Required: Plane mirror with stand, Corkboard, Colored pins, Protractor, Straight edge
Procedure:
Part A: The Law of Reflection
1. Place a sheet of paper on the corkboard.
2. Place the mirror on top of the paper as in the picture to
the right.
3. Look at one side of the mirror and locate the position
where the black support meets the mirror. Place a small
dot on the paper to mark this position. Repeat this step for
the other side of the mirror.
4. Remove the mirror from the paper and use a ruler to
connect the two dots. This line represents the position of
the mirror, since this is a rear surface mirror.
5. Replace the mirror on this line, such that the mirrored
surface lies along it.
6. Place a pin approximately 12 cm in front of the mirror
and approximately 7 cm to the right of center. Label this position "A."
7. Choose a point on the left side of the mirror and label it "B." Draw an eye at this position.
8. Position your eye behind the eye at position "B" such that the image from pin "A" is in line with the eye
at position "B."
9. In order to see the image of pin "A," a light ray has to leave pin "A" and reach your eye at position "B."
10. Use a straight edge or ruler to draw the path of the light ray as it leaves pin "A," reflects off the mirror,
and reaches your eye at position "B."
11. Draw a dashed line perpendicular to the mirror where the ray reflects from the mirror. This is called a
normal line.
12. Using a protractor, measure the angle of incidence and the angle of reflection. Enter them into a data
table.
13. Repeat steps 3-8 for 3 more positions (C, D, E) on the left side of the mirror.
14. Remove the mirror from the paper and use a straight edge to extend each of the reflected light rays
behind the mirror. Use dotted lines to illustrate that the light rays from pin "A" don't actually go through
the mirror.
Part B: Field of Vision
15. Place a pin approximately 4 cm in front of the center of the mirror.
16. Move your eye to the left side of the mirror until the image of the pin
is just at the edge of the mirror. Draw a small eye at this position.
17. Use a straight edge or ruler to draw the path of the light ray as it
leaves the pin, reflects off the mirror, and reaches your eye at this
position.
18. Move your eye to the right side of the mirror until the image of the
pin is at the edge of the mirror. Draw a small eye at this position.
19. Use a straight edge or ruler to draw the path of the light ray as it
leaves the pin, reflects off the mirror, and reaches your eye at this
position.
20. Repeat steps 15 – 19 for pin locations 8 cm and 12 cm away from the mirror.
Questions
1. Describe the relationship between the angle of incidence and the angle of reflection.
2. A 2.0 m tall woman wants to buy the shortest mirror that will allow her to view her entire body.
What height should the mirror be?
3. How high on the wall must the mirror hang? Explain.
4. Describe the image of pin "A." Where is it located relative to the mirror and to the actual pin? What
is its size compared to the actual pin?
5. Why does the eye "believe" that an image of the pin "A" exists behind the mirror?
6. Define field of vision in your own words.
7. What happens to the field of vision as an observer moves away from the mirror?
8. What determines the field of vision?
9. Sketch a top view of a car including the rear view and side view mirrors. Using your sketch, draw
the field of vision for each mirror. Label the "blind spots."