A mirror provides the most common pattern for specular reflection of light and usually consists of a pane with a metal coating where significant reflection occurs. The reflection is amplified in metals by suppressing the propagation of waves beyond their skin depths. Reflections also occur on the surface of transparent media such as water or glass. Previously, Lesson 3 dealt with the behaviour of waves moving along a rope from a denser medium to a less dense medium (and vice versa). The wave does not stop when it reaches the end of the middle. On the contrary, a wave will experience certain behaviors when it reaches the end of the middle. In particular, there will be a reflection outside the border and a certain transfer into the new medium. But what happens if the wave moves in a two-dimensional medium like a wave of water moving through seawater? Or what happens if the wave travels through the air in a three-dimensional medium such as a sound wave or a light wave? What behaviors can we expect from such two-dimensional and three-dimensional waves? In the diagram, the beam of light approaching the mirror is called the incident beam (denoted I in the diagram). The beam of light that leaves the mirror is called the reflected beam (denoted R in the diagram). At the point of incidence where the beam hits the mirror, a line can be drawn perpendicular to the surface of the mirror. This line is called the normal line (denoted N in the diagram). The normal line divides the angle between the incident beam and the reflected beam into two equal angles. The angle between the incident beam and the normal is called the angle of incidence.
The angle between the reflected beam and the normal is called the reflection angle. (Both angles are labeled with the Greek letter “theta,” accompanied by an index character; read “theta-i” for the angle of incidence and “theta-r” for the angle of reflection.) The law of reflection states that when a beam of light is reflected on a surface, the angle of incidence is equal to the angle of reflection. When light hits the surface of a (non-metallic) material, it bounces in all directions, due to the multiple reflections of microscopic irregularities inside the material (e.g., grain boundaries of a polycrystalline material or cellular or fibrous boundaries of an organic material) and through its surface when rough. It does not create an “image”. This is called diffuse thinking. The exact shape of the reflection depends on the structure of the material. A common pattern of diffuse reflection is Lambertian reflection, in which light is reflected in all directions with the same luminance (in photometry) or radiance (in radiometry), as defined by Lamber`s law of cosine. The study of waves in two dimensions is often carried out with a wave tank. A corrugated tank is a large, glass-bottomed water tank used to study the behavior of water waves. A light usually shines on the water from above, illuminating a sheet of white paper placed just below the tank. Some of the light is absorbed by the water as it passes through the tank. A ridge of water absorbs more light than a drinking trough.
Thus, the bright spots represent the troughs of the waves and the dark dots represent the ridges of the waves. As the water waves move through the wave tank, the dark and light spots also move. When the waves encounter obstacles in their path, their behavior can be observed by observing the movement of dark and light spots on the sheet of paper. Corrugated tank demonstrations are typically conducted in a physics class to discuss the principles underlying wave reflection, refraction, and diffraction. First, let`s look at the reflection, as shown in the diagram below for a light wave hitting a surface. We identify the incident ray as the incident ray and the outgoing radius as the reflected ray. At the same time, the angle ?i, which the incident ray makes perpendicular to the surface with a line (dotted in the diagram), is called the angle of incidence. The angle ?r of the reflected beam is called the reflection angle. When a longitudinal sound wave hits a flat surface, the sound is reflected consistently, provided that the dimension of the reflecting surface is large in relation to the wavelength of the sound. Note that audible sound has a very wide range of frequencies (from 20 to about 17000 Hz) and therefore a very wide range of wavelengths (from about 20 mm to 17 m). Therefore, the overall nature of the reflection varies depending on the texture and structure of the surface. For example, porous materials absorb some of the energy, and rough materials (where roughness is relative to wavelength) tend to reflect in many directions – dispersing energy rather than reflecting it consistently.
This leads to the field of architectural acoustics, as the nature of these reflections is crucial for the auditory sensation of a room. In the theory of external noise reduction, the size of the reflective surface easily distracts from the noise barrier concept by reflecting some of the sound in the opposite direction. Sound reflection can affect acoustic space. Practice problem: Complete the diagram to show (approximately) the trajectory of the beam when reflected from the mirror below. Water wave diffraction is observed in a harbor when waves bend around small boats and disturb the water behind them. However, the same waves cannot bend around larger boats because their wavelength is smaller than that of the boat. diffraction of sound waves is often observed; We perceive the sounds that are bent in the corners so that we can hear others talking to us from the neighboring rooms.
