Waves in a Ripple Tank
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As you investigate the properties of waves using the ripple tank, answer the following questions on a separate sheet of notebook paper and draw a sketch showing the behavior of the waves.
Part I—Reflection
A. Generate a straight pulse with the attachment with the long piece of wood. Place a barrier in the water so that it partially blocks the wave at an angle. Try blocking the wave with the barrier at different angles.
1. What is the relationship between the direction of the incoming wave and the reflected wave? Draw a sketch.
B. Replace the straight barrier with a curved one, with the concave side facing the wave generator.
2. Describe the shape of the reflected wave.
C. Find the point where the waves converge. This is called the focal point.
3. Sketch the waves coming to a focal point. Can you give another common example of waves being focused to a point?
Part II—Refraction
D. Change the depth of the water in the center of the tank by placing a piece of plastic on the bottom. Generate a straight wave with the long piece of wood so that the wave strikes the boundary of the two media (deep and shallow water) at an angle. Try varying angles.
4. Define refraction.
5. Is the wave speed faster or slower as it crosses the boundary into more shallow water?
6. What happens to the wave direction at the boundary?
7. How is the change in direction of the wave related to the wave speed?
8. How does the wavelength change as the wave crosses the boundary into shallow water ?
9. How does the frequency change as the wave crosses the boundary into shallow water?
Part III—Diffraction
E. Place a small barrier in front of a straight wave so that it intercepts only part of a wave front, and watch what happens at the edge of the barrier. Change the wavelength of the incoming wave by changing the speed of the motor, and again watch the edge of the barrier.
10. Define diffraction.
11. How does the wave interaction with the barrier vary with the wavelength, that is, do long wavelengths seem to diffract more than short wavelengths, or vice versa?
F. Place two long barriers in the tank leaving a small opening between them. Generate straight waves toward the opening and note the resulting pattern. Vary the size of the opening, and note how the pattern changes.
12. How does the angle by which the wave spreads out (diffract) depend on the size of the opening, that is, is there a larger angle of diffraction for a larger opening?
13. In what way does the spread of the diffraction pattern depend on the wavelength of the incoming waves, that is, is there more diffraction for larger wavelengths?
Part IV—Interference
G. Attach the two point source generators to the wave generator, place the tips in the water, and generate waves in phase . Change the frequency of the waves and observe the resulting patterns.
14. Define interference, antinode, and node.
15. How does changing the frequency affect the wave pattern?
16. How does changing the wavelength change the pattern?
Part V—Measuring Wavelength Using Interference
H. Using the two point sources as in part G, generate an interference pattern of nodes and antinodes.
The nodal lines represent points where the waves from the two point sources are 1/2 wavelength "out of phase," and the interfering waves cancel each other out. The antinodal lines represent points where the waves are "in phase," and maximum reinforcement occurs. This occurs when the distance from one point in the antinode is a whole number of wavelengths farther from one source than the other.
Draw a line down the shadow of the central antinode. Mark where the shadow of each point source is and draw a line connecting these points. Choose a point in the middle of the first antinode over from the central antinode.
Draw a perpendicular line from the central antinode line to the point on the first antinode. Label these lines x, d, and L as shown. Calculate the wavelength using the proportionality below.
