When waves encounter new mediums, barriers or other waves they can behave in different ways.
The characteristic of a wave striking a different medium and being bounced back, either totally or partially is termed reflection. There are two different ways in which a wave pulse can be reflected.
If the wave strikes the medium at an angle, the wave will be reflected at an angle, this is known as the Law of Reflection.
According to the Law of Reflection, the angle of incidence to the normal is equal to the angle of reflection to the normal where the normal being a ray perpendicular to the surface.
This type of reflection is characteristic of a wave striking a rough surface and being reflected randomly in all directions. For example, the paper reflects light in all directions. Therefore, you can read from any angle.
The reflection of sound is sometimes referred to as an echo. The percentage of sound reflected from a surface depends on the nature of the surface. For example, you get a high reflection rate from a rigid, smooth surface such as gym walls and low reflection from a soft, irregular surface such as soft irregular walls in a movie theatre.
The study of sound reflection is called acoustics.
Multiple sound reflections that cause the sound to be garbled are called reverberations.
When two or more waves occupy the same space at the same time they are said to interfere with each other. Since both waves are moving the interference will only last for a short length of time. At which point the two waves will continue on unchanged by the encounter. For that period of time when the waves are interfering with each other, they can do so in two distinct ways known as constructive interference and destructive interference.
Constructive interference results in a wave pulse that is bigger than either individual pulse i.e. they add together.
Destructive interference results in a wave pulse that is smaller than either individual pulse i.e. they subtract from each other.
The principle of superposition may be applied to waves whenever two or more waves are traveling through the same medium at the same time. The waves pass through each other without being disturbed.
The net displacement of the medium at any point in space or time is simply the sum of the individual wave displacements.
This is true of both waves and pulses.
When many similar waves occupy the same medium there is a continuous interference pattern which consists of both constructive interference and deconstructive interference. Under ideal circumstances, a standing wave can be established. A standing wave is exactly as its name implies a wave that appears to be motionless and is simply standing in one place.
In reality, there are many waves, all of which are moving but the overall pattern caused by the interference simply gives the appearance of a stationary wave. There are two main parts to the standing wave
Refraction of a wave occurs when a wave changes direction upon moving from one medium to another. Along with the change of direction, refraction also causes a change in the wavelength and the speed of the wave. The amount of change in the wave due to refraction is dependent on the refractive index of the mediums. One example of refraction is a prism. When white light enters the prism, the different wavelengths of light are refracted. The different wavelengths of light are each refracted differently and the light is split into a spectrum of colors.
Refraction can happen for either of the following circumstances
Refraction of light passing from air into glass
The ray of light entering the glass is termed the incident ray.
The ray that travels in the glass is termed the refracted ray.
The angle between the incident ray and the normal is called the angle of incidence.
The angle between the refracted ray and the normal is called the angle of refraction.
The incident ray strikes the glass at an angle and the refracted ray is bent “towards the normal”. Since the light ray bends towards the normal as it passes from air to glass (from less dense to denser), the angle of incidence is greater than the angle of refraction. When the light leaves the glass the ray is deflected “away from the normal”. In this case, the angle of refraction is greater than the angle of incidence (from more dense to less dense).
When the wave travels from a less dense to a more dense medium the angle of incidence is greater than the angle of refraction.
When the wave travels from a more dense to a less dense medium the angle of refraction is greater than the angle of incidence.
A prism uses refraction to separate the various colors of light composing the visible spectrum. This occurs because all the colors that make up white light do not travel at the same speed in glass thus, causing each color to bend different amounts.
This color separation is referred to as Dispersion. Rainbows work because the water drops act as tiny prisms.
You can usually hear a siren long before you see an emergency vehicle, because sound can bend around corners. This characteristic of bending around a corner is not a characteristic just for sound but for all waves in general and is known as the diffraction of waves.
Diffraction is the bending of waves around a barrier.
When a straight wave front strikes a barrier the component of the wave that is allowed to pass through the barrier will then become bent and appear as a circular wave.
The amount of bending depends primarily on the width of the opening. Maximum bending occurs when the width of the opening is approximately one wavelength.
Polarization is when a wave oscillates in one particular direction. Light waves are often polarized using a polarizing filter. Only transverse waves can be polarized. Longitudinal waves, such as sound waves cannot be polarized because they always travel in the same direction of the wave.
Absorption is when a wave comes into contact with a medium and causes the medium’s molecules to vibrate and move. This vibration absorbs or takes some of the energy away from the wave and less of the energy is reflected.
One example of absorption is black pavement which absorbs energy from light. The black pavement becomes hot from absorbing the light waves and little of the light is reflected making the pavement appear black. A white stripe painted on the pavement will reflect more of the light and absorb less. As a result, the white stripe will be less hot.
