Light: Refraction and Absorption

1. Light: Refraction and Absorption Vanderbilt Student Volunteers for Science Spring, 2008 Training Presentation

2. Introduction • Pass out the Instruction and Observations sheets • Write the following words on the board: • Refraction • Visible light • Electromagnetic spectrum • Laser • Absorption • Explain that light is a type of energy and is an electromagnetic wave (EM) • Stress that EM waves are transverse waves • Light is the only wave that can travel in a vacuum • Describe wavelength (distance from crest to crest) and give examples

3. Refraction • Give each group of students a jar containing water and a straw lying at an angle in the jar • Tell students to rotate the jar while looking at the straw and ask them what they observe • Tell students to unscrew the lid and to hold the straw vertically in the center of the jar so that it is half in/out of the water • Have them look at the straw through the side of the jar and slowly move the straw to either side of the jar (do not move the jar or your head) • Explain that the bending of light (refraction) occurs when light waves pass from one medium to another

4. Laser Demonstration • Center the laser on the groove of the ruler and place it on the 0 line of the observation sheet. • Turn on the laser and use the popsicle stick to show that the beam travels in a straight line. • Tell one student to hold the laser while another slides the empty refraction cup onto the paper within the half-circle. • Turn on the laser again and note that the beam comes out along the same line.

5. Laser Demonstration (Cont.) • Repeat steps 1 – 4 along the 45 line. • Note that the beam still travels in a straight line!

6. Refraction Cup • Tell students to pour water into the D-shaped refraction cup • Center the groove of the ruler on the 0 degree line, and find where the laser exits the cup (no refraction should occur at this angle, it should be along the 0 degree line) • Ask students why they think the path of the beam was not changed (medium changed, but angle is direct)

7. Refraction Cup (Continued) • Place the ruler and laser on the 45 degree line as done previously • Keep the laser in the same position and slide the water-filled refraction cup into its position • Mark the exit position with the red pen • Ask students why the beam did not exit out along the 45 degree line (the red laser was refracted)

8. The Appearing Coin • Place the styrofoam cup with the penny on the desk • Select one student in each group to pour the water while the other students in the group stand and observe the coin • Tell them to stand in a position where they can easily see the coin • Now have the students slowly back up until the coin has just disappeared from sight • Tell the designated student to slowly pour water into the cup • Tell students to raise their hands as soon as they can see the coin again

9. The Appearing Coin (Cont.) • Explain that refraction causes this effect • When water is added, the light is bent so that the coin becomes visible (light travels through one medium to another)

10. Absorption and Colors • Pass out the red and green filters • Have one student hold the red filter horizontally and another shine the red laser from above, pointing towards the desk or floor • Have students verify that the red laser light passes through the red filter • Repeat this with the green filter • Ask students to predict what will happen when the green laser light passes through the green filter and through the red filter • Explain that the filter only allows light of that wavelength to pass through Green Filter Red Filter Green Filter Red Filter

11. Absorption and Colors (cont.) • Optional Activity (If time permits) • Have students choose another colored filter (blue, aqua, yellow, or pink) • Ask them to predict whether their red laser light will be absorbed by the filter • The different colors will not block the laser entirely, so students should notice that the laser light dims when it passes through some of the filters

12. Review • Review basic concepts with students and collect all materials • Make sure that all lasers have been returned