Reflection of waves

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Definition of Reflection and Examples in everyday life

One characteristic of waves is experiencing reflection. Seawater waves propagate in the sea when they hit a rock then the wave reverse, so does the water wave in the water bath when it encounters a wall, the water wave reverses towards the direction it came from.

Examples of reflection experienced by sound waves are echoes and echoes. Reverberation occurs when sound is reflected while the sound source is still sounding. Usually, the echo occurs in an enclosed space. While the echo occurs when the sound is reflected after the sound source does not sound. Echo typically occurs outdoors and is not disturbing, but reverberation is frequently annoying because, for example, when someone is talking in a closed room, the reflection of the person’s voice off the walls causes the person’s speech to become blurred. To overcome this, often, on the walls of closed spaces such as auditoriums or music studios, air vibration dampers are installed that transmit sound so that sound is not reflected.

Waves that propagate on ropes, strings, or strings also experience reflection. For example, a wave on a guitar string that is played by a guitarist, after propagating along the strings, will be reflected when it arrives at the knot.

When propagating, waves carry energy so that if the waves are reflected after meeting an obstacle, some energy is passed on to the barrier and some are reflected. When a sound wave hits a wall, some sound energy is absorbed by the wall and some are reflected. Likewise, when a sea wave hits a rock or ship, some energy is transferred to the rock or ship hit by the wave, and some are reflected.

The Law of Reflection

Before understanding the law of reflection, first, learn the meaning of Rays and Wavefront. When drawing two or three-dimensional waves, the concept of wavefront is used. Waves that propagate on a rope or string are one-dimensional waves, waves that propagate on the surface of the water are two-dimensional waves, and waves that propagate in space such as sound waves are three-dimensional waves.

Reflection of waves 1

Wavefront represents two- or three-dimensional waves that propagate, while Rays are lines that are perpendicular to the wavefront.

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The Law of Reflection states that the angle of incidence is equal to the angle of reflection, as illustrated in the image below. The angle of incidence = the angle between the incident ray and the dotted line perpendicular to the reflecting surface. The angle of reflection = the angle between the reflected ray and the dotted line perpendicular to the reflecting surface.

Reflection of waves 2

Conceptual questions and answer about Reflection of waves

  1. What is wave reflection? Wave reflection is the phenomenon that occurs when a wave encounters a surface or boundary that does not absorb the wave’s energy and bounces the wave away from the surface.
  2. How is the angle of incidence related to the angle of reflection? The angle of incidence is equal to the angle of reflection. This is known as the law of reflection and it applies to all waves, including light, sound, and water waves.
  3. What is the law of reflection? The law of reflection states that when a wave is incident upon a surface, the angle of incidence is equal to the angle of reflection, measured relative to the normal at the point of incidence.
  4. What does the term ‘normal’ refer to in the context of wave reflection? In the context of wave reflection, ‘normal’ refers to an imaginary line that is perpendicular to the surface at the point where the incident wave strikes.
  5. Does the frequency of a wave change upon reflection? No, the frequency of a wave does not change upon reflection. Only the direction of the wave changes.
  6. What is the difference between specular and diffuse reflection? Specular reflection occurs when a wave hits a smooth surface and reflects in a single direction. Diffuse reflection, on the other hand, occurs when a wave hits a rough surface and the reflected waves scatter in many directions.
  7. What happens to the speed and wavelength of a wave when it is reflected? Upon reflection, the speed and wavelength of a wave do not change. Only the direction of the wave’s propagation changes.
  8. Why do we see our reflection in a mirror? We see our reflection in a mirror due to the law of reflection. When light waves from an object strike the mirror, they are reflected back at the same angle, creating a mirror image of the object.
  9. How is the principle of superposition related to wave reflection? The principle of superposition, which states that when two or more waves meet, their amplitudes (heights) add together, applies to reflected waves. If an incident wave and its reflection overlap, they will interfere according to this principle.
  10. Can sound waves be reflected? Yes, sound waves can be reflected. This is the basis for echolocation used by animals like bats and for technologies like sonar used in submarines.
  11. What is an echo? An echo is a reflection of sound that arrives at the listener so late that it is perceived as a distinct sound rather than an alteration of the original sound.
  12. Why do we not see our reflection in all types of surfaces? The reflection of light that allows us to see our own reflection depends on the smoothness of the surface. Specular reflection that produces a clear image requires a very smooth surface like a mirror. Rough surfaces scatter light in many directions, resulting in diffuse reflection.
  13. What is retroreflection? Retroreflection occurs when light or other waves are reflected directly back towards their source. This property is exploited in devices like cat’s eye reflectors on roads.
  14. What causes the red appearance of the sun at sunrise or sunset? The red appearance of the sun at sunrise or sunset is caused by a phenomenon called Rayleigh scattering, not by reflection. As sunlight passes through the Earth’s atmosphere, shorter wavelengths (blue and green) are scattered more than the longer wavelengths (red, orange, and yellow). When the sun is on the horizon, its light has to pass through more atmosphere, which scatters away most of the short-wavelength light and allows the red and orange light to reach our eyes.
  15. What is Brewster’s angle? Brewster’s angle is the angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface, with no reflection. It’s given by the formula θB = arctan(n₂/n₁), where n₁ and n₂ are the refractive indices of the first and second medium respectively.
  16. What is total internal reflection? Total internal reflection occurs when a wave incident on a boundary between two media is completely reflected back into the original medium. This happens when the wave is in a medium with a higher refractive index and hits the boundary at an angle larger than the so-called critical angle.
  17. What are standing waves and how are they related to reflection? Standing waves are wave patterns that appear to be stationary, typically as a result of interference between waves traveling in opposite directions. They are often produced by wave reflection, such as waves on a stretched string reflecting from the string’s fixed ends.
  18. What happens when a wave is reflected off a moving object? When a wave is reflected off a moving object, the frequency of the reflected wave can change depending on the relative motion of the source and the object. This is known as the Doppler effect.
  19. Is reflection of waves applicable only to light and sound? No, reflection of waves is a fundamental phenomenon that applies to all types of waves including light, sound, water waves, and electromagnetic waves such as radio waves and microwaves.
  20. How does a periscope work? A periscope works by using two mirrors arranged at 45-degree angles to the direction one wishes to see. The top mirror catches the incoming light rays and reflects them down to the bottom mirror which reflects the light directly into the viewer’s eye. This double reflection enables viewing over, around, or through objects and obstacles.

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