Reflection of Waves

Physics

definition

Incident, Reflected and Transmitted waves at a boundary

If a pulse is introduced at the left end of the rope, it will travel through the rope towards the right end of the medium. This pulse is called the incident pulse since it is incident towards (i.e., approaching) the boundary with the pole. When the incident pulse reaches the boundary, two things occur:
1.
A portion of the energy carried by the pulse is reflected and returns towards the left end of the rope. The disturbance that returns to the left after bouncing off the pole is known as the reflected pulse.

2.
A portion of the energy carried by the pulse is transmitted to the pole, causing the pole to vibrate.

example

Write the equation of reflected wave for a given incident wave at a rigid boundary

Example: Find the phase change between incident and reflected sound wave from a fixed wall by writing equations of incident and reflected wave.

Solution:
When a wave is reflected from a wall, the wave is inverted . As the phase difference between a wave and its inverted wave is , the phase difference is





example

Reflection of sound

Sound waves (like any other wave) return back in the same medium obeying the laws of reflection. The only requirement for the reflection of the sound wave is that the reflecting surface must be bigger than the wavelength of the wave. Reflection of sound wave is seen in echoes, megaphone, ear trumpet etc.

definition

Explain refraction of sound

Refraction of sound waves is most evident in situations in which the sound wave passes through a medium with gradually varying properties. For example, sound waves are known to refract when traveling over water. Even though the sound wave is not exactly changing media, it is traveling through a medium with varying  properties; thus, the wave will encounter refraction and change its direction. 

result

Equation of reflected wave for a given incident sound wave

Example: The displacement of the medium in a sound wave is given by the equation; where a & b are positive constants.
The wave is reflected by an obstacle situated at x = 0 . The intensity of the reflected wave is 0.64 times that if the incident wave. The equation for the reflected wave is given as  Find

Solution:
equation for sound intensity is








example

Reflection of a given incident sound wave in an open tube

Example: A train of sound waves is propagated along a wide pipe and it is
reflected from an open end. If the amplitude of the waves is 0.002 cm, the frequency 1000 Hz and the wavelength 40 cm, Find the amplitude of vibration at a point 10 cm from open end inside the pipe.

Solution:

Wavelength is 40cm
Amplitude to be found at 10 cm
In open pipe from open pipe at a distance of always a node is formed. So, amplitude at 10 cm from open end will be zero because amplitude at node is zero.

example

Incident, reflected and transmitted sound waves at a boundary

The simplest situation of reflection and transmission occurs when waves are impinging normal to the surface. The case of a longitudinal wave incident on the interface between two media is shown in the above figure.

law

Laws of reflection of sound

Law 1 : Incident wave,normal to the reflecting surface and reflected wave at the point of incidence all lie in the same plane.
Law 2: Angle of incidence is equal to the angle of reflection.

REVISE WITH CONCEPTS

Pulse Travelling Along a String With a Fixed/Open End

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Standing Waves and Normal Modes

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Important Questions
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