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Reflection of Waves

The reflection of waves is defined as the abrupt change in the wave's propagation direction after striking the interphase of the two distinct mediums. After striking the surface, the direction of the wave is changed, and the wave bounced back is called the reflected wave.

Like the incident wave, the reflected wave also travels along the principle axis with the alternate constructive and destructive patterns.

Unlike the reflection of light, the reflection of waves does not require a smooth and shining surface like a plane mirror. This reflected wave is caused by striking surfaces like plywood, metal sheet, wall, etc. It can be reflected by a rough and coarse surface as well.

There is just one requirement for the reflection of these waves to take place, and that is that the size of the reflecting surface must be larger than the wavelength of the sound wave.

Properties of the reflection of waves

Certain properties of the reflection of waves are mentioned below:

• The angle of reflection to the normal is the same as the angle of incidence to the normal.
• The incident ray, the reflected ray, and the normal at the point of incidence all three lie in the same plane.
• The reflected wave’s phase is not changed if the pulse rope is struck on a less dense medium.
• The phase of the reflected wave changes by 180 degrees if the pulse of the rope is struck on a medium that is quite dense.
• There may be a change in the intensity of the reflected wave, which is due to the partial refraction at the boundary surface that separates the two distinct mediums.

Various Types of Waves

There are many types of waves that exist. Some of them are mentioned briefly below:

• Longitudinal waves- These kinds of waves propagate in the same medium and in the same direction as that of the incident waves. The propagation of these waves includes alternate compressions and rarefactions. These waves can travel in solids as well as liquids.
• Transverse waves- These kinds of waves propagate in the perpendicular direction to that of the incident waves. These waves propagate by forming alternate crests and troughs. These waves can only travel through a solid medium.
• Electromagnetic waves- These waves are formed by the periodic and uniform, mutually perpendicular electric and magnetic fields, which are normal to the plane of the propagated wave. These behave like transverse waves, but unlike them, they can also travel in a vacuum and not just through solids. Light is an example of these types of waves.
• Reflection at an open boundary- When an incident wave is struck at an interface with an open end, then the wave undergoes partial refraction and reflection.
• Reflection at a closed boundary- When an incident wave is struck at an interface with a closed-end, then the wave undergoes only pure reflection.

Important Points of Reflection

Important points of reflection at a rigid or a closed boundary:

• Let us consider a string or a rope fixed at one end of the wall, and the other is kept loose.
• Now, when an incident wave or a pulse is generated from the free end of the wave, a force is acted on the wall.
• Because of Newton's third law of motion, the wall also exerts a force equal in magnitude and opposite in direction. The wall on the string exerts this force.
• Since the wall is a rigid body, it cannot exert the force back, making the attached string generate a pulse of the same magnitude in the opposite direction.
• In such a case, the phase difference between the two waves is 180 degrees.

Important points of reflection at a free boundary:

• In this case, the string or the rope is tied to a ring since it has an open end to it.
• Here, when the initial pulse strikes, the ring moves up and stretches the string. This makes the string produce a reflected pulse with the same sign and amplitude as that of the incident pulse.
• This results in creating a maximum displacement at the end of the string or the rope.
• There is no additional phase shift which is why the phase difference between the two waves is zero.

Reflection of waves has a great variety of usage in today's world, and there are many useful applications. Therefore, it is of great importance to learn about this branch of physics.

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