Physics 142
Name
12 points
Research Question:
Equipment:
Homework Due in Recitation Class, 9/26/00
Reci. Time 8:30
Fall, 2000
11;00
12;30
What is the relationship between the height a mirror needs to be
in order for you to see yourself and your distance away from
the mirror?
Full-length plane mirror, Measuring device (like a yardstick),
and An assistant.
To answer this question, conduct the following experiment:

Find a full-length, flat mirror (perhaps at home or at a department store or...).

You will be the object/observer and your assistant will help make the
measurements.

You will stand a certain distance (say about five feet) in front of the mirror, and look
at yourself.

Your assistant will hold a straight object (such as a meter stick) straight across the
mirror, parallel to the floor.

Your assistant should slowly raise (or lower) the meter stick until it is touching the
top of your head, as you see it in the mirror. Note this position. (Please do not write
on the mirror if it doesn't belong to you!)

Repeat the procedure to find the position where the meterstick is just touching the
tips of your toes.

Using these two measurements, determine the minimum mirror-length that allows
you to see your full body from that distance. Record all relevant data in a table.

Repeat these measurements for at least four other distances from the mirror.
1. Graph your data on a linear graph and describe the relation between the two
variables as precisely as possible.
2. Based on your data, how does the length of the mirror needed for you to see your
full image depend on your distance from the mirror?
3. How does the length of the mirror needed depend on your actual height?
4. Make a sketch of a large plane mirror and a "stick figure" representing a person.
Carefully draw a ray of light leaving the top of the person’s head and reflecting off
the mirror to the viewer’s eyes. Carefully draw a ray of light leaving the person’s
foot and reflecting off of the mirror to the viewer’s eyes. Keep in mind your law of
reflection, and make your drawing precisely.
5. To the same sketch, add a second ray diagram - for the same person at a different
distance from the mirror.
Physics 142
Name
Homework Due in Recitation Class, 9/26/00
Reci. Time 8:30
Fall, 2000
11;00
12;30
6. Does your sketch explain your answer to #3? Explain.
7. Why do you think clothing stores use mirrors that go from the floor to the ceiling in
their fitting rooms? Is this necessary for everyone to be able to see himself or
herself? Explain.