Reflection and Refraction

Reflection and Refraction Name ______KEY______

Physics Periods ______

Go To:

http://www.glenbrook.k12.il.us/gbssci/phys/Class/waves/u10l3b.html

HTTP://WWW.GLENBROOK.K12.IL.US/GBSSCI/PHYS/CLASS/WAVES/U10L3B.HTML

If a linear object attached to an oscillator bobs up and down 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 bright lines stretching across the paper and the troughs are the dark 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 above depicts a series of straight waves approaching a long barrier extending at an angle across the tank of water. The direction which these wavefronts (straight-line crests) are traveling through the water is represented by the arrow. The 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.

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? Perhaps you recall the ripple tank demonstration performed in class in which a rubber tube having the shape of a parabola was placed within the ripple tank.

The diagram at the above depicts such a parabolic barrier placed within 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 involves a change in direction of waves when they bounce off a barrier; refraction of waves involves a change in the direction of waves as they pass from one medium to another. Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves. It was mentioned previously that the speed of a wave is dependent upon the properties of the medium through which the waves pass. So if the medium (and its properties) are changed, the speed of the waves are changed. The most significant property of water which would effect the speed of waves traveling through it is the depth of the water. Water waves travel fastest when the medium is the deepest. Thus, if water waves are passing from deep water into shallow water, they will slow down. And as mentioned previously, this decrease in speed will also be accompanied by a decrease in wavelength. So as water waves are transmitted from deep water into shallow water, the speed decreases, the wavelength decreases, and the direction changes.

This boundary behavior of water waves can be observed in a ripple tank if the tank is partitioned into a deep and a shallow section. If a pane of glass placed in the bottom of the water, one part of the tank will be deep and the other part of the tank will be shallow. Waves traveling from the deep end to the shallow end can be seen to refract (i.e., bend), decrease wavlength (the wavefronts get closer together), and slow down (they take a longer time to travel the same distance). When traveling from deep water to shallow water, the waves are seen to bend in such a manner that they seem to be traveling more perpendicular to the surface. If traveling from shallow water to deep water, the waves bend in the opposite direction.

Reflection and Refraction Name ______

Physics Periods ______

Go To:

http://www.glenbrook.k12.il.us/gbssci/phys/Class/waves/u10l3b.html

HTTP://WWW.GLENBROOK.K12.IL.US/GBSSCI/PHYS/CLASS/WAVES/U10L3B.HTML

If a linear object attached to an oscillator bobs up and down 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 bright lines stretching across the paper and the troughs are the dark 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 above depicts a series of straight waves approaching a long barrier extending at an angle across the tank of water. The direction which these ______ (straight-line crests) are traveling through the water is represented by the arrow. The blue arrow is called a ______ 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:

______

______

______.

This is known as the ______.

Complete the Diagram Above

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? Think of a ripple tank demonstration in which a rubber tube having the shape of a parabola is placed within the ripple tank.

The diagram at the above depicts such a parabolic barrier placed within 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.

Complete the Diagram Above

Reflection involves a change in direction of waves when they bounce off a barrier;

______

______

______.

Refraction, or bending of the path of the waves, is accompanied by a change in speed and wavelength of the waves. It was mentioned previously that the speed of a wave is dependent upon the properties of the medium through which the waves pass. So if the medium (and its properties) are changed, the speed of the waves are changed. The most significant property of water which would effect the speed of waves traveling through it is the depth of the water.

______.

Thus, if water waves are passing from deep water into shallow water, they will slow down. And as mentioned previously, this decrease in speed will also be accompanied by a decrease in wavelength. So as water waves are transmitted from deep water into shallow water, the speed decreases, the wavelength decreases, and the direction changes.

This boundary behavior of water waves can be observed in a ripple tank if the tank is partitioned into a deep and a shallow section. If a pane of glass placed in the bottom of the water, one part of the tank will be deep and the other part of the tank will be shallow. ______

______

______.

When traveling from deep water to shallow water, the waves are seen to bend in such a manner that they seem to be traveling more perpendicular to the surface. If traveling from shallow water to deep water, the waves bend in the opposite direction.