RippleTank

2019 Name: _Ronaldo_Acosta_________________________________ Date: 4/7/21_______ Student Exploration: Ripple Tank Vocabulary: constructive interference, crest, destructive interference, diffraction, Huygens’ Principle, interference, law of superposition, node, refraction, trough, wave, wavelength Prior Knowledge Questions (Do these BEFORE using the Gizmo .) 1. The image below shows small ripples, or waves , moving through water in a pond. Circle the description below that you think describes the motion of a wave most accurately. A. Each wave consists of a set of water molecules moving outward from the center. B. When a wave passes, water molecules move up and down before returning to near their original position. 2. Waves have crests (high points) and troughs (low points). The wavelength of a wave is the distance between adjacent crests (or troughs). Label the crests, the trough, and the wavelength on the image at left. Gizmo Warm-up A ripple tank, such as the one shown in the Ripple Tank Gizmo, is a shallow pan of water with a vibrating motor that produces waves. The tank is lit from above so that the wave crests and troughs are visible. Ripple tanks are particularly useful because many properties of water waves are shared by other kinds of waves that are harder to see. Check that Open tank is selected and the Wavelength is 4.0 cm. Click Play ( ) and observe. Click Pause ( ) when the first wave reaches the right edge of the tank. 1. The light regions represent troughs while the dark areas represent crests. About how much simulation time does it take the wave to cross the tank? -_ Two seconds__ _________ 2. Click Reset ( ). Set the Wavelength to 16.0 cm, and click Play . Click Pause when the waves reach the edge. How did increasing the wavelength affect the shape and speed of the waves?

2019 The wave was open and moved faster. ( It took about one sec to cross.) Activity A: Wave motion Get the Gizmo ready : ● Select Barrier with 3-cm gap from the Scenario menu. Question: What causes wave motion? 1. Predict : In this activity, you will test two hypotheses for wave motion. Circle the hypothesis you think is closest to the truth. Predictions will change Hypothesis 1: Waves are sets of particles moving together due to their forward momentum. Hypothesis 2: Waves occur when particles transmit energy to other particles in all directions but don’t move far from their original positions. 2. Make connections : The hypothesis describes how some materials flow. For example, consider the mudslide shown at left. Compared to point A , point B is nearly three times farther from where the mudslide landed at the bottom of the mountain. Why did the mudslide miss point A but hit point B ? The front structure of the mudslide convey to point B. Which hypothesis is demonstrated by the motion of the mud? Hypothesis 1 3. Predict : The Gizmo shows a barrier with a small gap that waves can pass through. Points A and B are equal distances from the gap. A. If hypothesis 1 is true, which point do you think will be hit by a wave first? Explain. Point A will be hit first because the wave’s momentum right to left or left to right. B. If hypothesis 2 is true, which point do you think will be hit by a wave first? Explain. If it’s true, points A and B will be hit at the same time because it states that waves pass on energy throughout.

2019 springs on the side of the crest that fits within the gap can now spread out in a circle. These mini rolls now create the curved crest of the diffracted roll. Activity B: Diffraction Get the Gizmo ready : ● Click Reset . Check that the Barrier with 3-cm gap is selected and the Wave strength is 1.20. ● Remove the arrows from the tank. ● Set the Wavelength to 6.0 cm. Question: What factors control diffraction? 1. Investigate : Click Play , wait for the waves to reach the right side of the tank, and click Pause . Sketch the waves in the left picture. Click Reset , and repeat the procedure with the Barrier with a 6-cm gap selected. (You will have to set the Wavelength to 6.0 cm again.)

2019 2. Predict : Which wave to you think will diffract through a larger angle when it passes through a barrier with a 10-cm gap: A wavelength of 5.0 cm or a wavelength of 30.0 cm? Predictions will change or shift. 3. Test : Select the Barrier with a 10-cm gap . Play simulations with wavelengths of 5.0 cm and 30.0 cm. What do you notice? 5-cm wave did not refract as much as the 30-centimeter wave. 4. Summarize : In general, what is the relationship between diffraction and the ratio of wavelength to gap width? The more greater the ratio between gap width and the wavelength, the more the diffraction will be. 5. Apply : A typical sound wave has a wavelength of 1 meter. The wavelength of green light is about 500 billionths of a meter. Which type of wave will tend to diffract more through a narrow gap that is about 1 centimeter wide? Explain. Sound visible light more further than daytime because sound waves produce much higher wavelengths than light waves. Activity C: Interference Get the Gizmo ready : ● Select Single central source . Check that the Wavelength is 16.0 cm. ● Set the Wave strength to 1.00. Question: What happens when waves combine?

2019 B. Which region experienced destructive interference? Between points B and C 7. Observe Click Reset . Set the Wavelength to 32.0 cm and the Wave strength to 1.00. The sources shown in the Gizmo are 24 cm apart. Click Play . Focusing only on the area between the sources, drag arrows to two points where the depth never changes. These points are called nodes and experience destructive interference at all times. 8. Sketch : To understand the position of the nodes, consider the first image below. The image shows the waves produced by the left source on top and the waves produced by the second source on the bottom. “C” stands for crest, “T” for trough, and “N” for node. Note that the waves are in sync—crests are produced at both sources at the same time. In a certain period of time, both waves will move 4 centimeters. In the image below, label the crests, troughs, and nodes for each wave at this time. (Remember that the top wave moves to the right while the bottom wave moves to the left.) 9. Observe : In the second image, what do you notice at points 4 and 20? Both points, one of the crest meets a trough of some kind of the other wave 10. How do these points compare to the nodes you marked in the Gizmo? These locations are located throughout where the links are marked in the Gizmo. (Activity C continued on next page) Activity C (continued from the previous page)

2019 11. Analyze : In the previous example, points 4 and 20 are nodes because the two waves always cancel out at these points. If there is a crest from the first wave source, there is a trough from the second wave source. Consider the first node, at point 4. A. How far did the first wave travel to get to point 4? ___ 4 cm_ ______ B. How far did the second wave travel to get to point 4? __ 20 cm _____ C. What is the difference in these two distances? _____ 16 cm _____ D. How does this distance relate to the wavelength? __ Half of the wavelength _ In general, if the difference in distances is 0.5 wavelengths, 1.5 wavelengths, 2.5 wavelengths, and so on, the waves will interfere perfectly and the points will be nodes. 12. Calculate Click Reset . Change the Wavelength to 12.0 cm. Fill in the table below. (Note: x is the distance of a point from the left source.) Recall that the sources are 24 cm apart. x Distance wave must travel from the first source (cm) Distance wave must travel from a second source (cm) The difference in distances (cm) Distance difference Wavelength 3 3 cm 21 cm 18 cm 1.5 6 6 cm 18 cm 12 cm 1.0 9 9 cm 15 cm 6 cm 0.5 12 12 cm 12 cm 0 cm 0.0 13. Predict : Based on your chart, which distances from the first source will be nodes? Points 3 and 9 will be connections because the tides will be compensated by a shared wavelength beyond. 14. Test : Click Play and observe. The image at right is taken from the Gizmo with a distance scale superimposed. What do you notice? In picture points 3 and 9, as well as 15 and 21, give no motion of stream, Therefore, those features are lumps. 15. On your own : Interference occurs any time waves interact. Explore the interference patterns that occur in the Two gaps and Barrier at edge configurations in the Gizmo. Click the camera ( ) icon to take a snapshot of interesting interference patterns. Right-click the image, and click Copy Image. Paste the images into a blank word document to present your discoveries.

2019 The more lightweight the bottom of the stone is, the greater the difference in direction. (Activity D continued on next page) Activity D (continued from the previous page) 6. Predict : Select the Elliptical submerged rock . What do you think will occur to the waves as they move past this rock? What l think will occur to the waves when they move past this rock is Predictions will vary. 7. Observe Press Play . What did the waves do? What the waves will do is the tides will be directed collectively as they crossed the short rock. 8. Make connections : How does this scenario relate to the lenses of eyeglasses? Eyeglass cameras direct light in the equal way that the obscure rock concentrates on ocean streams. Analyze : Inactivity A, it was noted that each point on the crest of a wave can be thought of as the source of a new wave. In fact, a stronger statement can be made. Huygens’ Principle states that the wave formed by all those secondary waves acts exactly like the original wave. This means you can determine what the original wave will do by simply looking at the secondary waves spreading out from points on a crest. In particular, for each point on the crest, draw a curve representing the wave that will spread out from it. The edge formed by those “mini” waves shows how the whole wave will travel. The image at the right shows five points on the crest of a wave. A small circle drawn around the top shows a small wave coming out from it. It is a circle because the speed of the wave is the same all around it. Contrast that with the curve drawn around the bottom point. Outside the “Submerged rock” region, it is the same circle, but over the

2019 rock it is flattened because the wave moves more slowly there. Draw similar curves around the other 3 points and then draw a line connecting the right-most edge of each curve. This line describes the angle the wave will have when the water goes over the rock. Submerged rock