Waves will move from the center of vibration. Notice that the pattern spreads from the center and causes little ripples. This shows not only diffraction but also interference similar to that in station 2.
Answer: physical wave; diffraction Using a spoon, instruct students to hit the surface of the water in a pan of water. The ripples should be large enough to hit the end of the pie tin and reflect backwards. However, students might only see the spreading outward and call this diffraction.
One student should push back several of the coils and then release them. The waves will go down the slinky and reflect from the other end and bounce back. Answer: Physical wave, reflection. Instruct two students to extend the rope.
One should snap their wrist to create an oscillating wave. The wave reflects backwards when it hits the other student. Answer: physical wave, reflection Instruct students to shine a small beam of light through a prism in kit. If the light is angled correctly, they should get a rainbow effect. Also, put the prism on the laser light. This shows the refraction better.
Answer: electromagnetic light ; refraction Instruct students to shine a light on a mirror in kit. Students may also try the laser light. The light bounces off. Answer: electromagnetic light ; reflection If a beam of light is shone through a lens, the light will refract through the lens and create a different size image on the other side.
All electromagnetic waves:. Some types of electromagnetic waves, like radio waves, microwaves, infrared waves, visible light and ultraviolet waves, can be reflected and refracted. Refraction is caused by differences in the velocity of waves travelling through different substances. Electromagnetic waves form a continuous spectrum of waves. This includes:. So the bright spots represent wave troughs and the dark spots represent wave crests. As the water waves move through the ripple tank, the dark and bright spots move as well.
As the waves encounter obstacles in their path, their behavior can be observed by watching the movement of the dark and bright spots on the sheet of paper. Ripple tank demonstrations are commonly done in a Physics class in order to discuss the principles underlying the reflection, refraction, and diffraction of waves.
If a linear object attached to an oscillator bobs back and forth within the water, it becomes a source of straight waves. These straight waves have alternating crests and troughs. As viewed on the sheet of paper below the tank, the crests are the dark lines stretching across the paper and the troughs are the bright lines. These waves will travel through the water until they encounter an obstacle - such as the wall of the tank or an object placed within the water.
The diagram at the right depicts a series of straight waves approaching a long barrier extending at an angle across the tank of water. The direction that these wavefronts straight-line crests are traveling through the water is represented by the blue arrow. The blue arrow is called a ray and is drawn perpendicular to the wavefronts.
Upon reaching the barrier placed within the water, these waves bounce off the water and head in a different direction. The diagram below shows the reflected wavefronts and the reflected ray.
Regardless of the angle at which the wavefronts approach the barrier, one general law of reflection holds true: the waves will always reflect in such a way that the angle at which they approach the barrier equals the angle at which they reflect off the barrier. This is known as the law of reflection. This law will be discussed in more detail in Unit 13 of The Physics Classroom. The discussion above pertains to the reflection of waves off of straight surfaces.
But what if the surface is curved, perhaps in the shape of a parabola? What generalizations can be made for the reflection of water waves off parabolic surfaces? Suppose that a rubber tube having the shape of a parabola is placed within the water. The diagram at the right depicts such a parabolic barrier in the ripple tank.
Several wavefronts are approaching the barrier; the ray is drawn for these wavefronts. Upon reflection off the parabolic barrier, the water waves will change direction and head towards a point. This is depicted in the diagram below. It is as though all the energy being carried by the water waves is converged at a single point - the point is known as the focal point.
After passing through the focal point, the waves spread out through the water. Reflection of waves off of curved surfaces will be discussed in more detail in Unit 13 of The Physics Classroom.
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