Ok, I have below the materials and equipment needed so please become familiar with it.  Do some home research if you need clarification.

Materials and Equipment

To do this experiment you will need the following materials and equipment:

• several 1" × 3" glass microscope slides,
• diamond scribe or glass cutter,
• ruler,
• electrical tape,
• epoxy glue (either 5-minute or 30-minute epoxy),
• toothpicks,
• laser pointer,
• cardboard,
• tape,
• tape measure,
• paper,
• pencil,
• piece of string,
• sugar,
• water,
• graduated cylinder,
• gram scale, such as the Fast Weigh MS-500-BLK Digital Pocket Scale, 500 by 0.1 G
• calculator with trigonometric functions (sine, arctangent).

Experimental Procedure

Laser Pointer Safety

Adult supervision recommended. Even low-power lasers can cause permanent eye damage. Please carefully review and follow the Laser Safety Guide posted here.

Making the Prism from Microscope Slides

1. Figure 3, below, shows the sequence of steps you will be following to make a hollow glass prism in the shape of an equilateral triangle (from Edmiston, 1999). The prism will hold a liquid as you measure the liquid's index of refraction.
   

   Figure 4. Diagram of the sequence of steps for making a hollow glass prism (equilateral triangle) from microscope slides. The steps are explained below. (Edmiston, 1999)

2. The goal is an equilateral prism that can hold liquid. It will be constructed from microscope slides and epoxy.
3. Put a piece of black electrical tape across the face of the slide as shown above (Figure 4a). The tape should hang over the edge.
4. Score the other side of the microscope slide with a diamond scribe or glass cutter as shown (Figure 4a). Use a straightedge to guide the diamond scribe. The two scribe lines should be one inch apart and perpendicular to the long edge of the slide. (If desired, before scribing you can mark the positions for the scribe lines with marker. The marker can later be cleaned off with a small amount of rubbing alcohol on a paper towel.)
5. Now you will break the glass along the scribe lines. Hold the slide on either side of the first scribe line and bend the glass toward the taped side. Bend just enough to break the glass. Repeat for the second scribe line (Figure 4b).
6. Now bend the glass away from the tape, allowing the tape to stretch (Figure 4c). Continue bending until the triangle closes.
7. Place the prism on a flat surface to align the bottom edges. Use the overhanging tape to secure the prism in this configuration (Figure 4d).
8. Adjust the edges of each face so that they align correctly. At each apex of the prism, the inside edges should be in contact along their entire vertical length.
9. Follow the manufacturer's instructions for mixing the epoxy cement (usually you mix equal amounts from each of two tubes). Use a toothpick to apply epoxy to the inside corners of the prism to glue the three faces together (Figure 4e). The corners need to be water-tight, but keep the epoxy in the corners and away from the faces of the prism. Keep the bottom surface flat and allow the epoxy to set.
10. When the epoxy in the corners has set firmly, mix up fresh epoxy and use a toothpick to apply it to the bottom edge of the prism. Glue the prism to a second microscope slide as shown (Figure 4f). The bottom edge needs to be water-tight, but keep the epoxy away from the faces of the prism.
11. Allow the epoxy to set overnight, and then your prism will be ready for use.

Measuring the Index of Refraction of a Liquid

1. Figure 5, below, is a diagram of the setup you will use for measuring the index of refraction of a liquid. (Note that the diagram is not to scale.)
   

   Figure 5. Diagram of setup for measuring the index of refraction of a liquid using a laser pointer and a hollow triangular prism (not to scale; based on the diagram in Nierer, 2002).

2. The laser pointer should be set up so that its beam (dotted red line in Figure 5) is perpendicular to a nearby wall. You should attach a big piece of paper to the wall for marking and measuring where the beam hits. The height of the laser pointer should be adjusted so that it hits about half-way up the side of the prism. The laser pointer should be fixed in place. Check periodically to make sure that the beam is still hitting its original spot.
3. When the prism is empty (filled only with air), then placing it in the path should not divert the beam. Mark the spot where the beam hits the wall when the prism is empty. When the prism is filled with liquid, the laser beam will be refracted within the prism (solid blue line). The emerging beam (solid red line) will hit the wall some distance away from the original spot of the undiverted beam. You will measure the distance, x, between these two points (see Figure 5).
4. Figure 6, below, is a more detailed view of the prism which illustrates how to measure the angle of minimum deviation, θ_md. You need to mark points a, b, and c in order to measure the angle. Points a and b are easy, because they are project on the wall. Marking point c is more difficult, because it is under the prism. The next several steps describe how to mark point c.
   

   Figure 6. Detail diagram showing how to measure the angle of minimum deviation (not to scale; based on the diagram in Nierer, 2002).

5. Tape a sheet of paper to the table, centered underneath the prism.
6. With the prism empty, on the sheet of paper mark the point where the beam enters the prism (point d in Figure 6). Then mark the point where the beam exits the prism (point e in Figure 6). Later you will draw a line between d and e to show the path of the undiverted beam.
7. On the wall, mark the point where the undiverted laser hits (point b in Figure 6). (As long as the laser pointer stays fixed, this point should be remain constant throughout your experiment. It's a good idea to check it for each measurement.)
8. Now add liquid to the prism. You want to rotate the prism so that the path of the refracted beam within the prism (solid blue line from d to fin Figure 6) is parallel with the base of the prism. (A pinch of non-dairy creamer in the liquid can help you visualize the beam within the prism, and should not have a significant effect on the index of refraction of the liquid.) When the prism is rotated correctly, mark the position of the emerging beam on the paper on the wall (point a in Figure 6). On the paper on the table, mark the point where the beam emerges from the prism (point f in Figure 6).
9. Now you can move the prism aside. Leave the paper taped in place.
10. Use a ruler to draw a line from point d to point e. This marks the path of the undiverted beam.
11. Next, you want to extend a line from point a (on the wall) through point f (on the table). To do this, stretch a string from point a so that it passes over point f. Mark the point (c) where the string crosses the line between d and e.
12. Measure the distance, x, between points a and b, and record it in your data table.
13. Measure the distance, L, between points b and c, and record it in your data table.
14. The distances you have measure define the angle of minimum deviation, θ_md. The ratio x/L is the tangent of the angle. To get the angle, use your calculator to find the arctangent of x/L. (The arctangent of x/L means "the angle whose tangent is equal to x/L.") Record the angle in your data table.
15. Now that you have the angle of minimum deviation, you can use equation 4 to calculate the index of refraction, n, of the liquid in the prism.
    
16. To check that your setup is working, plain water should have an index of refraction of 1.334.

Standard Sugar Solutions for Comparison

1. Use the following table for amounts of sugar and water to use in order to make 5%, 10%, and 15% sugar solutions.

   desired concentration	amount sugar (g)	amount water (mL)
   5%	5	95
   10	10	90
   15	15	85

2. Measure the index of refraction of each sugar solution.
3. Now measure the index of refraction of a solution with unknown sugar concentration (e.g., a clear soft drink or fruit juice). If you measure a carbonated beverage, make sure that there are no bubbles in the path of the laser (gently dislodge them from the side of the glass, if necessary).
4. With the index of refraction of the unknown solution, combined with the data you have from your known sugar solutions, you should be able to estimate the sugar concentration of the unknown solution.

Variations

• Compare the index of refraction of regular and diet soda. Is there a difference?
• Can you use index of refraction to measure different the concentration of salt dissolved in water? Make salt solutions with different known concentrations and find out. If you live near a body of salt water, can you use this method to estimate the salt concentration of salt water samples from different locations? This would be especially interesting to measure where fresh and salt water meet, e.g., in a tidal estuary where a river or stream meets a bay or the ocean.
• Advanced. Slowly pour water containing a pinch of non-dairy creamer over a layer of sugar crystals in the bottom of an aquarium, trying not to allow too much turbulence to develop in the water. Wait for an hour or two to allow a concentration gradient to form as the sugar crystals dissolve. Predict what will happen when a beam of light shines through the solution. Shine a laser pointer through the solution. Can you account for the path that the beam follows in the liquid? (http://www.sasked.gov.sk.ca/docs/physics/u3c12phy.html)

Sources

• Edmiston, M.D., 2001. "A Liquid Prism for Refractive Index Studies," Journal of Chemical Education 78(11):1479–1480, [accessed October 2, 2006] available online at: http://www.jce.divched.org/hs/Journal/Issues/2001/Nov/clicSubscriber/V78N11/p1479.pdf.
• Nierer, J., 2002. "Using the Prism Method," [accessed September 25, 2006] http://laser.physics.sunysb.edu/~jennifer/journal/prism.html.
• Soderstrom, E.K., 2004. "How Does Sugar Density Affect the Index of Refraction of Water?" California State Science Fair Abstract [October 2, 2006] http://www.usc.edu/CSSF/History/2004/Projects/J1533.pdf.

Career Focus

If you like this project, you might enjoy exploring related careers.

	Physicist Physicists have a big goal in mind—to understand the nature of the entire universe and everything in it! To reach that goal, they observe and measure natural events seen on Earth and in the universe, and then develop theories, using mathematics, to explain why those phenomena occur. Physicists take on the challenge of explaining events that happen on the grandest scale imaginable to those that happen at the level of the smallest atomic particles. Their theories are then applied to human-scale projects to bring people new technologies, like computers, lasers, and fusion energy.			Physics Teacher Our universe is full of matter and energy, and how that matter and energy moves and interacts in space and time is the subject of physics. Physics teachers spend their days showing and explaining the marvels of physics, which underlies all the other science subjects, including biology, chemistry, Earth and space science. Their work serves to develop the next generation of scientists and engineers, including all healthcare professionals. They also help all students better understand their physical world and how it works in their everyday lives, as well as how to become better citizens by understanding the process of scientific research.
	Photonics Technician Do you enjoy watching cable television, texting on your phone, and surfing the Internet? Do you know anyone who has had eye surgery and been back to normal the next day? Many of the advances in telecommunications and medicine are due to laser and fiber-optic technology. This technology has led to devices that provide faster and richer communication, advanced surgeries, and faster healing times, as well as amazing robotics for manufacturing. But, as with all equipment, someone has to install and maintain it. That is what photonics technicians do. These professionals are responsible for building, installing, testing, and maintaining optical and fiber-optic equipment such as lasers, lenses, and optics systems. Photonics technicians contribute to the technology that has drastically changed how we communicate and how we live.