Name: __________Madison Morson____________ Date: _______May 17, 2021________
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? _____2s_______
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?
_____It made the wave wider and faster
Get the Gizmo ready:
Activity A:
• Select Barrier with 3-cm gap from the Scenario
Wave motion
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.
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?
______Because the momentum of the mudslide
was moving in the direction of point B not
A.__________________
_________________________________________
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.
___________A because the momentum of the wave is
moving in the direction of
A_________________________________
____________________________________________
B. If hypothesis 2 is true, which point do you think will be
hit by a wave first? Explain.
____________________________________________
____________________________________________
(Activity A continued on next page)
Activity A (continued from previous page)
4. Observe: Check that the Wavelength is 9.0 cm, the Wave strength is 1.20, and the waves
are Planar. Drag arrows (found on the left side of the Gizmo) to the positions of points A
and B on the diagram. Press Play. Click Pause when the first wave reaches point A.
A. What do you notice about the shape of the wave after it passes through the barrier?
____After it passes the barrier in turns into a circle shape
_______________________________________________________________
___________________________________________________________________
B. Do the waves reach point A first, point B first, or do they reach points A and B at
about the same time? __It reached A and B at the same
time_______________________________________________
5. Infer: What do your observations suggest regarding the two hypotheses? ______Neither
hypothesis was correct._________
_________________________________________________________________________
The ability of waves to spread from a point such as the gap in the barrier is called
diffraction. This ability allows waves to turn corners in ways that individual particles cannot.
The fact that waves reached point B at the same time as point A demonstrates that waves in
water move differently from the mud in the landslide.
6. Challenge: Water waves are caused by individual water molecules moving back-and-forth
and up-and-down locally. Because the particles do not move in sync, water piles up in some
places and troughs appear in other places. The individual molecules themselves do not
move very far compared to the wave we see.
Water piled up in one region (a crest), tends to drain into nearby regions. In fact, each
individual point on a crest can be thought of as the source of a new wave. This idea, called
Huygens’ Principle, was discovered by the great 17th-century Dutch physicist Christiaan
Huygens.
Use Huygens’ Principle to explain how water waves can diffract. If you like, draw a sketch to
illustrate your point and attach it to this worksheet.
__________Water waves can diffract while piled up in one region and drain into
another._______________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
_________________________________________________________________________
Get the Gizmo ready:
Activity B: • Click Reset. Check that the Barrier with 3-cm gap
is selected and the Wave strength is 1.20.
Diffraction
• 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 6-cm gap selected. (You will have to set the Wavelength to 6.0 cm again.)
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?
___5cm_______
3. Test: Select the Barrier with 10-cm gap. Play simulations with wavelengths of 5.0 cm and
30.0 cm. What do you notice? ______the 30cm wave poured into the other region
faster.___________________________________________
_________________________________________________________________________
4. Summarize: In general, what is the relationship between diffraction and the ratio of
wavelength to gap width? _____the wavelength that’s smaller than the gap _____will diffract
more__________________________________________
_________________________________________________________________________
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.
The green light because if the wavelength is smaller than the gap then it will diffract more
_________________________________________________________________________
_________________________________________________________________________
