Ripple While You Work

 

I.               Discussion: Although water waves are not the simplest waves, they are familiar to everyone. Observing the behavior of water waves in a ripple tank will introduce you to the analysis of wave motion. The purpose of this lab is to observe wave phenomena in a ripple tank

II.             Materials

a.     Ripple tank with light and butcher paper underneath

b.     Dowel

c.     Paraffin blocks

d.     Medicine dropper

e.     Curved Metal

f.      Wave generator

g.     Glass plate and washers

III.           Procedure:

a.     Step 1: The ripple tank is set up. BEFORE adding water, place a piece of butcher paper UNDER the tank. Place a stopper in the hole. Fill the tank with water using the plastic container. The water should just be coming up the sides. If foam is in the tank, make sure it is totally wet.

b.     Step 2: Use an eye dropper to add drops of water one at a time to the tank.

                                               i.     QUESTION 1: What is the shape of the waves?

                                             ii.     QUESTION 2: Does the speed the waves seem to be the same in all directions?

c.     Step 3: Place the dowel in the water. Produce a straight wave front by rolling the dowel forward 1 cm, with the flat of your hand.

                                               i.     QUESTION 3: What is the shape of the wave?

d.     Step 4: Place a paraffin block in the tank. With the dowel generate a pulse that strikes the barrier straight on.

                                               i.     QUESTION 4: What does the wave do when it reaches the barrier?

                                             ii.     QUESTION 5: After the wave strikes the barrier, what is the new direction of the wave?

e.     Step 5: Move the paraffin block to change the angle at which the pulse strikes it.

                                               i.     QUESTION 6: What is the shape of the reflected pulse?

f.      Step 6: Produce circular wave pulses with the dropper so that they reflect from the paraffin block.

                                               i.     QUESTION 7: What is the shape of the reflected waves?

                                             ii.     QUESTION 8: From what point do the reflected waves appear to be originating?

g.     Step 7: Take out the paraffin block and place the curved piece of metal into the tank instead. Use the dowel to make straight waves that reflect from the metal barrier.

                                               i.     QUESTION 9: What do you observed when you use this parabolic reflector?

h.     Step 8: Find the point at which the straight pulses reflected by the metal barrier meet and mark it on the paper under the tank with your finger. This is the focus of the parabola. Generate a circular pulse with the dropper held straight above the focus of the parabola.

                                               i.     QUESTION 10:  What is the shape of the reflected pulse?

                                             ii.     QUESTION 11: Do any other points gibe the same pulse shape?

i.      Step 9: Adjust your paddle on the wave generator so that it just touches the surface of the water. Slowly turn on your generator and then turn it to the lowest setting to produce a steady wave. Change the frequency slowly and observer.

                                               i.     QUESTION 12: What effect does increasing the frequency have on the wavelength?

j.      Step 10: Place a paraffin barrier halfway across the middle of the tank. Observe the part of the straight wave that strikes the barrier as well as the part that passes by it. Adjust the frequency of the wave generator so that the combination of the incoming and reflected wave appears to stand still .the combination then forms a standing wave.

                                               i.     QUESTION 13: How does the wavelength of the standing wave compare to the wavelength of the wave traveling past the barrier?

k.     Step 11: Support a piece of glass with rubber stoppers so that it is 1.5 cm from the bottom of the tank and its top is just covered with water. Arrange the glass so that incoming wave fronts are parallel to one edge of the glass.

                                               i.     QUESTION 14: What happens as the waves pass from deep to shallow water?

l.      Step 12: Now turn the glass so that its edge is no longer parallel to the incoming wave fonts.

                                               i.     QUESTION 15: Are the wave fronts straight both outside and over the glass?

                                             ii.     QUESTION 16: How do the speeds of the waves compare?

m.   Step 13: Place paraffin blocks across the tank until they reach from side to side with a small opening in the middle. Generate straight waves with the wave generator.

                                               i.     QUESTION 17: How does the straight wave pattern change as it passes through the opening?

n.     Step 14: Using a piece of paraffin about 4 cm long, modify your paraffin barrier so that it has two openings about 4 cm apart near the center. Generate a straight wave and allow it to pass through the pair of openings.

                                               i.     QUESTION 18: What wave pattern do you observe?

o.     Step 15: Put two point sources about 4 cm on the bar of the wave generator. Turn on the wave generator. Turn on the wave generator to produce overlapping circular waves.

                                               i.     QUESTION 19: What pattern do you now observe?