Lab - Reflection from a Plane Mirror
Part I 1) Obtain a laser pointer and a plane mirror attached to a block of wood.
2) Place the mirror on a piece of paper. Trace an outline of the mirror. Make sure not to allow the
mirror to move from this outline.
3) Shine the laser at the mirror. Stick a pin along the path that the ray from the laser travels making
several holes in the paper both before and after the ray hits the mirror.
4) Carefully trace the path of the incident beam and the reflected beam on the paper.
5) Move the laser and repeat for 3 different incident angles. Make sure each person in the group
has at least 1 trial for their own lab folder!
6) Using a protractor, draw a normal line for each place where the laser hits the mirror.
7) Now measure both the incident and reflected angles.
Questions:
1. What is the relationship between the incident and reflected angles?
2. Does the light reflect off the front surface or back surface of the mirror? Is there any evidence of
this from your experiment?
Part II –
1) Place the plane mirror on a second sheet of paper on the cardboard. Trace around the mirror so that
if it moves it can be replaced to its former position.
2) Stick a pin approximately 8 cm from the mirror into the paper. This is the object pin. Label the pin
with an O. Where do you think the image is?
3) You will locate the image by parallax. Have your partner put a pencil behind the mirror at various
locations until you find the point that as you move your head from side to side the pencil and the
image move together. If they move together, they must be in the same location. You have located the
image by parallax.
3. Where is the image - in front of, behind or on the surface of the mirror?
4.
Measure the distance from the object to the mirror and the distance from the image to the mirror.
5. How do the distances of the image and object from the reflecting surface compare, di and do?
Practice
1. The diagram represents a light ray being reflected from a plane mirror. The angle between the
incident ray and the reflected ray is 70.°.
What is the angle of incidence for this ray?
2. A ray of light strikes a mirror at an angle of incidence of 60°. What is the angle of reflection?
3. In the diagram, a light ray leaves a light source and reflects from a plane mirror.
At which point does the image of the source appear to be located?
A.
B.
C.
D.
A
B
C
D
4. When a ray of light strikes a mirror perpendicular to its surface, what is the angle of reflection?
5. Parallel light rays are incident on the surface of a plane mirror. Upon reflection from the mirror, the
light rays will
A. converge
B. diverge
C. be parallel
D. be scattered