Exploration Guide: Laser Reflection
Vocabulary: Telescope, optics, adaptive optics, plane, mirror, degrees, laser,
reflect, horizontal, ideal, beam, θ, angle of incidence, reflect, perpendicular
Prior Knowledge: How a ball bounces. How one plans a shot on
a billiard table. Looking in a mirror. Ricochet.
Warm-up:
Visible light waves range from a ______________ of 400nm- _________nm.
Some of the energy that reaches _________________ from the sun is
________ light. Visible light from the sun is white ____________. White
light has all the color of a rainbow combined and it looks _________ to us,
unless it goes through some sort of ______________________. Light from
the ________________________ in your home and the fluorescent
_________ in the school is ______________light.
Light travels in a straight _______________ unless the material that
the light travels through doesn’t change. So, a beam of light shining through
the air is usually _________________. One way to change the direction of a
beam is by __________________. Reflection is the bouncing ____________
of light rays when they _______________ an object. But the light does not
change directions randomly. There is a _____________ of _____________.
Activity A:
Reflection From an Ideal
Mirror
In this activity, you will examine reflection from a
plane mirror. In the Gizmotm, select Ideal mirror
from the dropdown menu. Be sure that Laser
On/Off is checked and all other options in the
Gizmo are unchecked.
What you see is a laser beam striking a mirror and being
________________. The laser always comes in as a _______________ line.
The mirror can be _______________________, using the Angle slider.
Use the Angle slider to vary the angle of the mirror. Describe how the
reflected beam changes when the angle of the mirror increases or decreases.
Set the Angle of the mirror to 0 degrees. (To set a slider to a specific value,
type the number in the field to the right of the slider and hit Enter.) Describe
the reflected laser beam.
If the angle of incidence is 41 degrees, then the angle of reflection will be
_____
Describe the reflected beam when Angle is set to negative values.
If the angle of incidence is -55 degrees, then the angle of reflection will be
_____________
Set the Angle to any value other than 0 degrees. Then grab the laser and
drag it up and down to different positions. How does this affect the reflected
beam?
How does it affect the angle between the incoming beam and the reflected
beam?
Set the Angle to 25 degrees and check Show normal. A normal line is
perpendicular to a plane from any viewpoint. Also shown are two angles, θI
θI (theta i) refers to the angle of ___________________, the
angle that the incoming ray makes with the normal. θr (theta r) refers to
and θr.
the angle ___ _____________________, the angle that the reflected ray
makes with the normal.
How does the size of the angle of incidence compare with the size of the
angle of reflection?
How do the angle of incidence and the angle of reflection compare with the
angle of the mirror?
How does the angle formed by the incoming beam and the reflected beam
compare with the angle of the mirror?
Set the Angle to 30 degrees. Then check Insert beam splitter.
How do the seven incoming beams compare to one another? How do they
compare to the single beam that exists when the beam splitter
is not present?
How do the reflected beams compare to one another?
Grab the laser and drag it up and down to several different positions.
Describe the effect that this has on the incoming beams and the
reflected beams.
Reflection From Non-Ideal Mirrors
In this activity, you will examine reflection from some mirrors that are not
perfect planes and, based on that reflection, sketch the shape of the mirror.
From the dropdown menu, select Ideal mirror. Check Laser On/Off and
Insert beam splitter. All other options should be unchecked.
Set the Angle of the mirror to 0 degrees. Describe the appearance of the
rays that are reflected from the mirror.
Change the Angle to 20 degrees and describe the reflected rays.
Return the Angle to 0 degrees and select Mirror 1 from the dropdown
menu. The surface of this mirror is not a perfect plane (not perfectly
flat and smooth). You will experiment to find the angles on its surface
at several locations.
Describe the appearance of the reflected rays. How do they compare to
the reflected rays from the ideal mirror?
Uncheck Insert beam splitter and turn on Show protractor and Show
center beam angles. Then drag the laser to its uppermost
location, at Laser location = 35 cm. Describe the reflected ray
from this point on the mirror. What must be the angle of the
spot on the mirror's surface where this beam strikes it?
Slide the laser down to Laser position = 30 cm. Describe the reflected
ray from this point on the mirror. What must be the angle of the
mirror's surface at this spot?
Continue moving the laser downward in 5 cm increments and determine
the angle of the surface of the mirror at each point. When
you've gathered data for the entire range of the laser's possible
positions, use this data to sketch the shape of the surface of the
mirror.
Set the dropdown menu to Mirror 2. Be sure the Angle of the mirror is
still 0 degrees. Repeat the process of determining the angle of various
spots along the mirror.
Make a sketch of the surface of the mirror, just as you did earlier. When
you're done, return the laser to its location at 0 cm .
Check Insert beam splitter. Explain the reflection based on your sketch
of the mirror's surface.
Turn the beam splitter OFF and set the dropdown menu to Mirror 3. Again,
with the Angle of the mirror at 0 degrees, repeat the process of
determining the shape of the mirror. This time, position the laser at 3
cm increments. Then return the laser to its central position (Laser
location = 0 cm).
The beam splitter separates the single laser beam into seven parallel
beams about 6.25 cm apart. Make a sketch of what you think
the incoming and reflected rays that will look like when you
insert the beam splitter.
Check Insert beam splitter and check your expectations.
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