Download Refraction and Reflection Lab

Reflection and Refraction Lab
MSED 250
Purpose:
To explore light interaction with planar and nonplanar mirrors and lenses.
Materials:
Power supply
Light box optical set
Meter stick optic bench
Optic bench light
Optic bench
Procedure:
1. The following diagram depicts a ray of light striking the surface of a plane mirror.
Describe the path that you expect the reflected light beam to take.
2. Place the 4-slit gate in the holder and observe how the light beams reflect off the
mirror. If you were to replace the plane mirror in front of the beams with a
white piece of paper, like an index card, would the paper also reflect light?
Write down your thoughts.
a. Place a white card in place of the mirror. Now take a second sheet of paper
and hold it in front of the card on which the light beams are striking. Try
to catch any reflection off the first card with the second. Can you see any
evidence that the light lines from the first card are being reflected on
the second?
b. If you can or cannot see evidence, provide a reason why this may be
so?
1
3. The 4-slit gate effectively makes parallel light beams. The light beams look like
this:
a. How could you use plane mirrors to make the individual light beams
all meet at one point?
b. Would this also work if, instead of four separate beams, you had one
broad beam?
c. Another way to do this is to use a curved mirror. Set up the light box with
the four slit gate. There are two curved mirrors in the light box kit. A
concave mirror can also be used in place of plane mirrors to bring light
beams to a common focus. Determine the focal distance (the distance from
the mirror to the focus point) for both mirrors.
i. Highly curved mirror Focal distance = _____ cm.
ii. Lesser curved mirror Focal distance = _____ cm.
Refraction
Light bends when it passes from one medium to another.
4. Examining refraction
a. Set up the light box with the narrow single slit gate
b. Place the Lucite rectangle in front of the light beam with the light entering
through one of the longer sides.
c. Rotate the rectangle in both directions
i. In what position must the rectangle be in order to see no light
bending?
ii. Where does light bending occur?
iii. Note what happens as you rotate the rectangle away from this
position:
2
1. Does the angle of refraction stay the same? Explain.
2. Does the intensity (brightness) of the refracted beam
stay the same? Explain.
3. Does the width of the refracted beam stay the same?
Explain.
d. Replace the rectangle with the Lucite triangle.
i. Let the light beam enter the triangle perpendicular to one of the
faces, but not centered on the face.
1. What do you observe? Remember our conversations
regarding diamonds. Can you see reflection and internal
reflection?
2. Slowly rotate the triangle. At some point the white light
will be bent to the point that the white light is separated
into its spectral colors.
a. Which color gets bent most?
b. Which color gets bent least?
c. Which color is on the outside of a rainbow?
d. Which shape, the rectangle, the equilateral
triangle, or the 30-60-90 triangle provides the
greatest separation of color? Why do you think
this is so?
e. Is there any difference in the “quality” of the
rainbow if you replace the narrow single slit with
the wider one? How about if no gate is present?
e. Replace the single light gate with the 3-slit gate and the triangle with the
half circle, with the flat side facing and perpendicular to the light gate.
i. What do you observe?
3
ii. What happens if you rotate the half circle to the right or left?
iii. Predict what you will see if you were to turn the half circle
completely around so that the light struck the curved surface first.
Write your prediction and then try it.
iv. Explain the results
v. What two factors are necessary for a light beam to refract?
Gemstone Refraction Index Determination
One of the most important tools in identifying gemstones is the refractometer. This tool
allows you to determine the refractive index of the polished surfaces of gemstones. A
high R.I. liquid is used to make an airless contact between the stone and a piece of calcite
in the refractometer. The stone is moved along the calcite until a green band is seen.
Check out the demonstration stations to see if you can identify the two gemstones.
Gemstone 1:
Gemstone 2:
Lenses
Recreate the pinhole device from the previous lab using the meter stick optic bench,
lamp, screen, and opaque card.
1) Speculate what would the image on the screen would be like if you placed
a biconvex lens in place of the pinhole.
2) Configure the optic bench as noted above. (You may need to adjust the
distance from the lens to the screen.) Alternate between the pinhole and the
lens. Note your observations here. Can you explain your observations?
How do the results compare?
Which of the illustrations below best describes how light acts when it travels
through the lens, or are they all accurate, or are they all wrong? You can check your
thoughts here.
4
3) Use the lens and arrange the apparatus so the screen displays a sharp upside
down image that is the same size as the bulb. Keep the lens in place, but move
the screen, first closer to the lens, then farther from it. Describe what
happens.
4) Replace the lens with the pinhole and repeat the movement of the screen.
Compare the results with those discovered when you used the lens.
5) Put the lens back in place and adjust the screen so the image is in sharp focus.
i. What do you think will happen to the image on the screen if you use a
card to cover the top half of the lens? Write your prediction below.
ii. Perform the experiment and note your observations. Do they agree
with your prediction? Can you explain what you see?
iii. Would it make any difference if you covered the center of the lens
and left the outer parts clear?
5