Name______

Four Important Properties of Waves

1.  Reflection: waves will bounce off a reflecting surface at the same angle they hit it

2.  Refraction: waves bend when they go from one medium to another

3.  Diffraction: waves bend around obstacles and openings

4.  Interference: when two waves hit, they add together if crests overlap and subtract if troughs overlap

1. Reflection

Materials: White paper, large hardcover book, flat mirror, laser pointer, ruler, protractor

Directions:

  1. Stand a hardcover book up and open it slightly so it stays standing up.
  2. tape the flat mirror to the cover of your textbook. Make sure it is at the bottom of the cover so that the bottom of the mirror is touching the table.
  3. On a white piece of paper, use a protractor and ruler to draw a straight line across the center of the paper. Make sure the line is at a right angle (90 degrees) to the edge of the paper. On one side of the line write “IN” and on the other side write “OUT.”
  4. Lay the paper on the desk and line-up the bottom of the paper along the bottom of the mirror. The line you drew should hit the middle of the mirror. Make sure the edge of the paper is exactly against the bottom of the mirror. Tape the paper down with one or two pieces of tape.
  5. Turn out the lights in the room.
  6. Shine the laser pointer at the mirror from an angle on the side that says “IN.” Hold it slightly above the table so that you can see the laser beam on the white paper. Make the beam hit the mirror exactly where the line you drew hits the mirror. WARNING: Never look directly into a laser beam or you could damage your eyes. Do not point the laser at other students.
  7. While one student holds the laser steady, another student should trace the laser beam on the paper. Trace both the incoming beam and the reflected beam.
  8. Turn off the laser pointer.
  9. Using a protractor, measure the angle between the “IN” beam and the center line, and the “OUT” beam and the center line.
  10. Repeat this for three different angles.


ANGLE IN (degrees) ANGLE OUT (degrees)

ANGLE 1: ______

ANGLE 2: ______

ANGLE 3: ______

What do you notice about the angle in and the angle out?

______

If there was a slight difference between the two angles, why do you think this is?

______

2. Refraction

Materials: Glass, water, pen or pencil, lenses, white paper, hardcover book, ruler

PART 1

Directions:

  1. Open a hardcover book slightly and stand it on your desk. Tape a white piece of paper on the cover.
  2. Turn out the lights in the room and leave one door or window open.
  3. Hold up a lens between the bood and the door or window, and move the lens in and out from the book to try to get a focused image on the paper.
  4. One student should hold the lens steady while another student uses a ruler to measure the distance between the lens and the book in centimeters. This is the focal length of the lens.

DIAMETER (cm) FOCAL LENGTH (cm)

LENS 1: ______

LENS 2: ______

LENS 3: ______

PART 2

Directions:

Fill a clear glass with water and place a pen or pencil in it so that half the pen or pencil is in the water and half is out of the water.

Describe what you see:

______

Why does it look this way?

______

3. Diffraction

Materials: Plactic tubs, water, blocks of metal, eye dropper

Directions:

Fill a plastic tub with a small amount of water. Place two blocks of metal in the tub so that there is a small opening between them. Use the eye dropper to drop one drop of water behind the opening.

Draw what you see on the other side of the opening:

What happens to the laser when half of it is blocked with a piece of foil?

______

Why does this happen? ______

Why can’t you see diffraction with a flashlight and a book? ______

______


4. Interference

Interference is what happens when two waves come together. Crests (which are above zero, or positive) will add, and troughs (which are below zero, or negative) will subtract.

Here is an example:

Wave 1: ______

Wave 2: ______

Interference: ______


Now you try it! Draw the wave that would result when the following pairs of waves interfere:

Wave 1: ______

Wave 2: ______

Interference: ______

Wave 1: ______

Wave 2: ______

Interference: ______

Wave 1: ______

Wave 2: ______

Interference: ______

Draw what the laser looked like when a hair was held in front of it:

Why do we have to use a hair?

This material was developed through the Cornell Science Inquiry Partnership program (http://csip.cornell.edu), with support from the National Science Foundation’s Graduate Teaching Fellows in K-12 Education (GK-12) program (DGE # 0231913 and # 9979516) and Cornell University. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF.