Lesson 3: Wave Behavior (PDF)

9/23/2024 Lesson 3 Wave Behavior  9/23/2024 Focus Question What happens when two waves meet?  9/23/2024 New Vocabulary incident wave standing wave re...

9/23/2024 Lesson 3 Wave Behavior  9/23/2024 Focus Question What happens when two waves meet?  9/23/2024 New Vocabulary incident wave standing wave reflected wave wavefront principle of superposition ray interference normal node law of reflection antinode refraction  9/23/2024 Review Vocabulary tension: the specific name for the force exerted by a rope or a string  9/23/2024 Waves at Boundaries When a wave encounters the boundary of the medium in which it was travelling, some or all of the wave can: Reflect back into the medium Pass through the boundary into another medium, often changing direction at the boundary  9/23/2024 Waves at Boundaries The wave that strikes the boundary is called the incident wave. If some of the energy of the incident wave is reflected backward, the returning wave is called the reflected wave. Whether the reflected wave is upright or inverted depends on the characteristics of the two mediums.  9/23/2024 Superposition of Waves The principle of superposition states that the displacement of a medium caused by two or more waves is the algebraic sum of the displacement caused by the individual waves. When waves combine, they can cancel or form a new wave of lesser or greater amplitude. The result of the superposition of two or more waves is called interference.  9/23/2024 Superposition of Waves  9/23/2024 Superposition of Waves A point that does not move is nodes called a node. antinode A point that has the largest displacement is called an antinode.  9/23/2024 Superposition of Waves A standing wave is a wave that nodes appears to be standing still, antinode produced by the interference of two waves moving in opposite directions.  9/23/2024 Waves in Two Dimensions When you throw a small stone into a calm pool of water, you see the circular crests and troughs of the resulting waves spreading out in all directions. You can sketch those waves by drawing circles to represent the wave crests.  9/23/2024 Waves in Two Dimensions If you dip your finger into water with a constant frequency, the resulting sketch would be a series of concentric circles, called wavefronts, centered on your finger. A wavefront is a line that represents the crest of a wave in two dimensions. It can be used to show waves of any shape, including circular waves and straight waves.  9/23/2024 Waves in Two Dimensions Wavefronts drawn to scale show the wavelengths of the waves, but not their amplitudes. Two-dimensional waves always travel in a direction that is perpendicular to their wavefronts. That direction can be represented by a ray, which is a line drawn at a right angle to the crest of the wave.  9/23/2024 Waves in Two Dimensions A ripple tank can be used to show the properties of two-dimensional waves. Vibrating boards produce waves with long, straight wavefronts.  9/23/2024 Waves in Two Dimensions A rigid barrier placed in the ripple tank will reflect waves. This can be modeled by a ray diagram. The orientation of the barrier is shown by a line, called the normal, which is drawn perpendicular to the barrier.  9/23/2024 Waves in Two Dimensions The angle between the incident ray and the normal is called the angle of incidence. The angle between the normal and the reflected ray is called the angle of reflection. The law of reflection states that the angle of incidence is equal to the angle of reflection.  9/23/2024 Waves in Two Dimensions A ripple tank can also model the behavior of waves as they travel from one medium into another. For example, the water in one part of the tank might be shallower than the water in the rest of the tank. This shallow water acts like a different medium.  9/23/2024 Waves in Two Dimensions As the waves move from deep to shallow water, their speed decreases, and the direction of the waves changes. The change in the direction of waves at the boundary between two different media is known as refraction.  9/23/2024 Waves in Two Dimensions Because the waves in the shallow water are generated by the waves in the deep water, their frequency is not changed. Based on the equation λ = v/f, the decrease in the speed of the waves means that the wavelength is shorter in the shallower water.  9/23/2024 Quiz 1. Which is the term for the point on a standing wave that does not move? A trough C antinode B wavefront D node CORRECT  9/23/2024 Quiz 2. The result of the superposition of two or more waves is called A reflection B refraction C interference CORRECT D a standing wave  9/23/2024 Quiz 3. In which of the cases shown in the diagram would the resulting wave at the dotted line point down? A none of them B 1 C 2 D 3 CORRECT  9/23/2024 Quiz 4. In a ray diagram, the orientation of the barrier in a ripple tank is shown by a line drawn perpendicular to the barrier, called the: A normal CORRECT C wavefront B reflected ray D incident ray  9/23/2024 Quiz 5. The law of the reflection states that the angle of incidence is ________ the angle of reflection. A greater than C equal to CORRECT B less than D 45° ±