amplitude, constructive interference, destructive interference, diffraction, frequency, fundamental frequency, phase angle, and superposition.

When two waves meet they create a third wave that is a combination of the other two waves. This third wave is actually the sum of the two waves at the points where they meet. The two original waves are still there and will continue along their paths after passing through each other. After passing the third wave no longer exists.

**Step 1:** Place a wall at an angle in the
window. Run the program.

Note the angle at which the waves strike the wall and the angle at which they are reflected. The angle between the incident wave and the normal is called the angel of incidence. The normal is the line that is perpendicular to the interface. The angle between the reflected wave and the normal is called the angel of reflection. You can measure these angles with a protractor.

**Step 2:** Record (draw a picture) your
findings.

**Step 3:** Stop the run and change the
angle of your wall. Run the program and observe the change.

*What can you conclude about the relationship
between angle of incidence and angle of reflection?*

**Step 4:** Repeat using a parabolic
barrier. To do this change the wall to a lens. Set the angle left and right
to 60. Leave everything else the same. Note the lens can not be rotated
to any angle, it is always straight on with the wave.

Run the program. Draw a picture of the resulting pattern.

*Does the angle of incidence equal the angle
of reflection? Explain why or why not?*

**Going further:
**Change the barrier again only this time
place two walls at right angles to each other so that their corners are
touching. Again make a picture of the resulting pattern.

*What happened this time to the wave angles?*