Reflection of Waves

# Reflection of Waves

## Introduction:

Reflection of waves: We are constantly confronted with scenarios involving wave reflection; for example, in the phenomena of echo, sound reflected from the distant object hits the listener with a slight delay. We’ll learn more about wave reflection from a fixed and free end in this section.

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When a wave collides with a surface, a portion of the wave is reflected while the rest is transmitted into the second medium. The transmitted wave can also be referred to as a reflected wave if the wave is incident obliquely on the boundary. The incident and refracted waves are subject to Snell’s Law of Refraction, whereas the incident and reflected waves are subject to the rules of reflection.

## A brief outline:

Progressive waves follow the same rules as light waves when it comes to reflection. A progressive wave’s reflection from a boundary surface is affected by the nature of the boundary surface. The reflection at the surface can be one of two sorts, depending on the circumstances of the progressing wave. Reflection at the hard wall occurs when a progressive wave going through a rarer barrier is reflected from a denser medium, while Reflection at the free end occurs when a progressive wave traveling through a denser medium is reflected from a rare medium. The phase of reflected sound waves of rough surfaces and the reflection of string waves at their ends affects whether the reflected and incident waves will interfere constructively or destructively. There is a phase reversal for string waves near the ends of strings, which is vital for generating resonance in strings. The appearance of propagation is lost because the reflected and incident waves add to each other as moving in opposite directions, and the resulting vibration is named a standing wave.

### Important concepts:

#### Reflection (Fixed end):

• Ponder the case of a string that is attached to a sturdy wall at its right end. When a pulse is allowed to propagate along these strings, it approaches the right end and is reflected, as seen in the diagram above.
• The pulse exerts a force on the wall when it reaches the fixed end, and the wall, according to Newton’s third law, exerts an opposite and equal force on the string. This second force causes a pulse to be generated at the support, which then moves back along the string in the opposite direction as the incident pulse. There is no displacement at the base in this type of reflection because the string is fixed there.
• At that time, the reflected and incident pulses acquire opposite signs and cancel each other out. The reflection of a moving wave at a rigid boundary occurs with a phase reversal or a phase difference in the case of a hard boundary.

#### Reflection (Free end):

• We call it a free end once the right end of the string is connected to a ring that moves up and down on a rod without friction. When the pulse reaches the right end of the rod, the ring advances up the rod, pulling on the string and stretching it, creating a reflected pulse with the same sign and amplitude as the original pulse.
• The incident and reflected pulses reinforce each other in such a reflection, resulting in the maximum deflection at the end of the string: the ring’s maximum displacement is twice the amplitude of either of the pulses.
• As a result, there is no additional phase shift in the reflection. The reflection of a travelling wave at an open border occurs without any phase shift.
• To summarise the foregoing result, we can state that waves are reflected appropriately at a boundary between two media. A travelling wave is reflected with a phase reversal at a stiff boundary or a closed-end, while it is reflected without a phase shift at an open boundary.
• If the incident wave is described mathematically as y i (x, t) = a sin (kx – t), then the reflected wave is expressed mathematically as

yr (x, t) = a sin (k x + ωt + П) = – a sin (k x + ωt)

The reflected wave is illustrated as when the wave is reflected at an open border.

a sin (k x + ωt) = yr (x, t).

When a pulse hits the end of a medium, what happens to it? Yet if the medium is set in space or free to travel at its end determines the result.

A barrier between two media, as well as an object which will reflect the wave, induce reflection. A mirror, a metal sheet, or just air can be used as the object. The border can be solid (such as a wall), liquid (such as water), or gaseous (such as air) (like air). When an object is a level and perpendicular to the incoming wave’s direction, reflection occurs. When this happens, every portion of a single wavelength reflects back at the same angle.

## Significance of Reflection of waves in NEET exam:

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Question 1: What is the purpose of reflection? Who came up with it?

Answer: Reflection’s purpose is to offer information about the thing, to reflect light, and to serve as protective layers. Its creator is unknown, but its use is thought to date back to antiquity.

Question 2: What is the process of reflection?

Answer: In general, there are two forms of reflection: specular and diffuse reflection. Smooth surfaces such as metal, glassware, liquid, and polished stone reflect light in a mirror-like manner. Light scatters in various directions as it meets with a rough surface, resulting in diffuse reflection.

Question 3. Once specular or diffuse reflections occur, what actually occurs?

Answer: They cause the observer’s visual system to produce an image! Because light bounces off one side of an object and back to the eye via the other, the eye sees it through its surface! The brain deduces from this that there has to be an imaginary object behind or in the real one, resulting in an image! Humans can learn about their environment by looking at images produced by reflections in this way! Nowadays, technologies such as televisions use a similar concept, but instead of projecting sound, they transmit visuals.

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