Light: Refraction

Davidson Student Volunteers for Science

Spring 2011

Introduction• Pass out the Instruction and Observations sheets• Write the following words on the board:

– refraction, visible light, electromagnetic spectrum, transverse waves• 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

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

Laser Demonstration1. Center the laser on the groove

of the ruler and place it on the 0 line of the observation sheet.

2. Turn on the laser and use the popsicle stick to show that the beam travels in a straight line.

3. Tell one student to hold the laser while another slides the empty refraction cup onto the paper within the half-circle.

4. Turn on the laser again and note that the beam comes out along the same line.

Laser Demonstration (Cont.)

• Repeat steps 1 – 4 along the 45 line.

• Note that the beam still travels in a straight line!

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)

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)

Review

• Review basic concepts with students and collect all materials

• Make sure that all lasers have been returned

Credit: Vanderbilt Students Volunteer for Science