PHY124
Lab # 10
Name ___________________
Reflection and Refraction
Lab Partners:
Purpose: The purpose of this lab is to study reflection and refraction of light.
Apparatus
Plane Mirror
Triangular shaped piece of glass
Rectangular shaped piece of glass
2 Pins
1 Ruler
1 Sheet of cardboard
1 Protractor
Procedure Part A
Reflection
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1) Draw a line across the middle of a sheet of plane white paper.
It should be parallel to the top of the sheet. Label it XY.
2) Stand the mirror up perpendicular to the page and against the textbook. Attach the mirror to
the textbook with tape.
3) Draw a point on a sheet of paper in front of the mirror. Label this location point A.
4) Place the sheet of paper on top of the cardboard and insert a pin upright into the sheet of paper
at point A.
5) Place the mirror and block on top of the sheet of the paper so that the reflecting surface of the
mirror is on top of line XY.
6) Place the ruler on its edge on top of the sheet of paper.
7) Look down the edge of the ruler and adjust it so that it points towards the reflection of the pin
in the mirror.
8) Draw a line along the edge of the ruler. Label this line A'.
9) Extend this line to where it crosses the line XY. Label the point of intersection point D.
10) Draw a line that is perpendicular to XY at point D. Label this line DE.
11) Draw a line from point D to point A.
12) Measure and record the angle ADE with the protractor.
Angle ADE is
________________ degrees.
13) Measure and record the angle of line A'DE with the protractor.
Angle A'DE is
________________ degrees.
Procedure
Part B
Refraction
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1) Place a piece of white paper on top of the sheet of cardboard.
2) Place the rectangular piece of glass in the middle of the sheet of paper.
3) Trace the outline of the glass on the paper.
4) Place a needle vertically into the paper next to the glass rectangle at a distance of about
one-fourth the way across the back of glass.
5) Place the second pin vertically into the paper at a distance of about 2 inches away from the
first pin and in line with the side edge of the glass.
6) Look at the edge of the glass and find the angle at which the image of the second pin lies
directly behind the image of the pin up against the glass.
7) Place the edge of the ruler on the paper and line it up with the image of the two pins. Again
adjust the position and angle of the ruler so that the image of the fist pin blocks out the image of
the second pin.
8) While carefully holding the ruler so that it does not move, draw a line along the edge of the
ruler on the paper. This line represents the light ray that exits the glass.
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9) Remove the glass from the paper.
10) Draw a straight line from the edge of where the glass was out along the path of the two
needles that are in the cardboard. This represents the light ray that entered the piece of glass.
11) Draw a line connecting the ends of the light ray that entered and exited the glass. This
represents the path of the light ray inside the glass.
12) Using the protractor, measure and record the angle formed between the light ray and the
normal at the point where it entered the glass. This is θ1.
13) Using the protractor, measure and record the angle formed between the light ray and the
normal at the point where it exited the glass. This is θ4.
(Note: The angles measured in steps 12 and 13 should be the same size.)
14) Using the protractor, measure and record the angle formed between the light ray inside the
glass and the normal at the point where the light ray entered the glass. This is θ2.
15) Using the protractor, measure and record the angle formed between the light ray inside the
glass and the normal at the point where the light ray exited the glass. This is θ3.
16) Using Snell's Law, calculate the index of refraction for the glass using θ1 and θ2.
Procedure Part C
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1) Place a new sheet of plain white paper on the cardboard.
2) Place the triangular piece of glass in the middle of the paper so that one of the points is
directly facing you with the flat side directly opposite you.
3) Trace the outline of the piece of glass on the paper.
4) Stick a pin vertically into the paper next to the glass near the middle of the backside of the
glass.
5) Hold a second pin next to one of the back corners of the glass.
6) Look at the edge of the glass and position yourself so that the pin in the cardboard sticks up
right above the corner of the glass nearest you.
7) Slide the second pin straight back until its image falls directly behind one of the images of the
first pin. Stick this second pin down into the cardboard at this location.
8) Using the ruler as in steps 7 and 8 of part A, draw a sight line representing the light ray exiting
the glass that is aligned with the two pins in the cardboard.
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9) Move the glass off the top of the paper.
10) Using the ruler, draw the lines that represent the light path outside of the glass. (Draw a
straight line from the first pin out beyond the second pin.)
11) Draw the light path that represents the ray as it traveled through the glass.
12) Using the light rays drawn measure the angles for the angle of incidence and the angle of
refractance for the side of the triangle where the light ray entered the glass triangle. Then
determine the index of refraction for the glass triangle.
Procedure Part D
1) Place a new piece of white paper on top of the cardboard.
2) Place the glass triangle on the paper so that one of the flat sides is towards you and a point is
one the opposite side.
3) Trace the outline of the glass onto the paper.
4) Hold a pin near the back corner of the glass triangle.
5) Slide the pin towards you along one of the side to a point about one third of the length of one
of the sides of the glass.
6) Hold a second pin near the front corner of the glass triangle on the side where the first pin is.
7) Slide the second pin straight back until it's image appears to hide behind the image of the first
pin.
8) Using the ruler as in steps 7 and 8 of part A, draw a sight line on the paper to the point where
the image of the two pins appear to exit the glass.
9) Draw the lines that trace out the path of the light ray from the pins to your eye. Include in the
sketch below the approximate location of the path for the light ray as it traveled inside the glass
triangle.
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Note: For Part D of this lab you do not have to measure the angles for the light rays. You simply
have to be able to explain what the path of the light ray is while inside the glass triangle.
Question for Lab # 10 Reflection and Refraction
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1) How close did the angle of incidence come to the angle of reflectance in Part A? (You need to
calculate the percent error.)
2) Was the material that the rectangular piece of glass made out of the same as the material used
to make the triangular shaped piece of glass? What makes you think so?
3) Explain what happened to the ray of light as it passed through the glass triangle. (For both Part
C and Part D tell me why it followed the path that it did based upon the index of refraction of the
glass and air.)
4) Using the index of refraction that you calculated for the rectangular shaped piece of glass,
what is the speed of light in this material?
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