University of Virginia Physics Department Refraction A Physical Science Activity

Student Activity

Materials

• Transparent, rectangular container at least 4 cm deep, or rectangular glass plate
• Cardboard at least 10 cm longer and wider that the plastic conainer
• 4 straight pins
• Ruler
• Protractor

Procedure

1. Place water in a transparent rectangular container to a depth of 3 cm.
2. Place the container on the cardboard and mark the outline of the container on the cardboard.
3. Place a pin in the cardboard behind the container. The pin should be as close to the container as possible.
4. Place a second pin 4 to 5 cm behind the first. The two pins should form a straight line which should form an angle of less than 45° with the side of the container.
5. Bend down in front of the container, so that you are looking at the two pins through the water in the container. Place a third pin in front of the container close to it. This pin should appear to line up with the two pins behind the container.
6. Place a fourth pin 4 to 5 cm in front of the third pin so that it lines up with the other pins. Readjust the positions of any of the pins so they all appear to be in a line when you look through the water in the container.
7. Carefully remove the container of water, leaving the pins in their position.
8. Use a ruler to draw a line connecting the positions of the two pins that were behind the container. Repeat this procedure for the two pins that were in front of the container.
9. Draw a third line inside the area were the water container was located connecting the other two lines. This line represents the path of the light ray through the water.
10. With a protractor, measure the angle between the two sides of the container and the lines connecting the two pins that were behind the container.
11. Repeat step 11 for the line connecting the two pins in front of the container.

Data Sheet

Angle Measured Measurement of Angle Angle between pin line and the front side of the container     Angle between pin line and the back side of the container     Angle between the line inside the tray connecting the two pin lines and the side of the container     Questions:  1. Did the light bend toward or away from the side of the container as it entered the water?    2. Did the light bend toward or away from the side of the container as it left the water?   3. Were the angles measured in steps 10 and 11 equal?   4. How did the direction of the light ray entering the water compare to the direction of light leaving the water?   5. A light ray enters a piece of glass from air at an angle of 35 degrees. Use the diagram below to answer the questions. a. At what angle did the light ray leave the glass? b. Draw the line inside the glass representing the path of light inside the glass. c. Are the angles between the light rays and the surface of the glass smaller inside or outside the glass? d. When the angles between the light rays and the surface of the glass become larger, does that represent light speeding up or slowing down?