Though a sound wave does not consist of crests and troughs, they do consist of compressions and rarefactions. These principles of reflection can be applied to sound waves. The more similar the medium, the more transmission that occurs. And if a heavy rope is attached to another heavy rope (two very similar media), little reflection and mostly transmission occurs. So if a heavy rope is attached to a light rope (two very dissimilar media), little transmission and mostly reflection occurs. Conversely, the less similar that the two media on each side of the boundary are, the more reflection that occurs and the less transmission that occurs. The more similar that the two media on each side of the boundary are, the less reflection that occurs and the more transmission that occurs. The amount of energy that becomes reflected is dependent upon the dissimilarity of the two media. If the rope is not attached to a pole but rather resting on the ground, then a portion of the energy is transmitted into the air (the new medium), causing slight disturbances of the air particles. If the rope is attached to a pole (as shown at the right), the pole will receive some of the energy and begin to vibrate. A portion of the energy carried by the pulse is transmitted into the new medium.The disturbance that returns to the left is known as the reflected pulse. A portion of the energy carried by the pulse is reflected and returns towards the left end of the rope.Upon reaching the end of the medium, two things occur: A pulse moving through a rope will eventually reach its end. In that unit, it was mentioned that there are two types of reflection for waves on ropes: fixed end reflection and free end reflection.
In Unit 10 of The Physics Classroom, the boundary behavior of a pulse on a rope was discussed. Later in Lesson 3, diffraction, transmission, and refraction will be discussed in more detail. In this part of Lesson 3, the focus will be upon the reflection behavior of sound waves. There are essentially four possible behaviors that a wave could exhibit at a boundary: reflection (the bouncing off of the boundary), diffraction (the bending around the obstacle without crossing over the boundary), transmission (the crossing of the boundary into the new material or obstacle), and refraction (occurs along with transmission and is characterized by the subsequent change in speed and direction). The behavior of a wave (or pulse) upon reaching the end of a medium is referred to as boundary behavior. When one medium ends, another medium begins the interface of the two media is referred to as the boundary and the behavior of a wave at that boundary is described as its boundary behavior.
As a sound wave travels through a medium, it will often reach the end of the medium and encounter an obstacle or perhaps another medium through which it could travel.