A wave is a moving, dynamic disturbance (variation from equilibrium) of one or more physical quantities. In periodic waves, those physical quantities repeatedly vibrate about a stable (resting) value at some arbitrary frequency. When the whole waveform travels in one direction, it is considered to be a travelling wave. In contrast, a couplet of superimposed periodic waves moving in polar directions results in a standing wave. In this type of wave, the vibration’s amplitude has nulls at some locations where the wave’s amplitude looks smaller or even zero. Waves are generally described by wave equations.
A longitudinal wave is a type of mechanical wave in which the medium’s oscillation is parallel to the direction in which the wave moves, and the medium’s displacement is in the same direction as that of the wave’s propagation. Longitudinal waves are also known as compression or compressional waves because these waves generate rarefaction and compression when propagating through a medium. They are also called pressure waves as they cause a decrease and increase in pressure. A wave formed along the spring toy, where the length between coils enlarges and shrinks, is a good example. Naturally occurring longitudinal wave examples include seismic P-waves (produced by explosions and earthquakes) and sound waves (particles moving as pressure waves in an elastic medium). The sound produced by a tuning fork is a perfect example of sound waves existing in a longitudinal direction. In a sound wave, the amplitude is the distance between the pressure of the disturbed medium and the maximum pressure generated by the wave. The speed of sound relies on the composition, type of propagation medium, and the temperature via which the sound travels.
Longitudinal Waves Questions with Answers
1) What is a wave?
A wave is a moving, dynamic disturbance (variation from equilibrium) of one or more physical quantities. In periodic waves, those physical quantities repeatedly vibrate about a stable (resting) value at some arbitrary frequency.
2) What is a plane wave?
A plane wave is a significant mathematical concept about a wave where the disturbance is similar along any plane normal to the particular direction of propagation. Analytically, the most basic wave is in the class of sinusoidal plane waves. In this case, at any location, the field encounters simple harmonic movement at one frequency. In one-dimensional media, complex waves can typically be split as the sum of numerous sinusoidal plane waves possessing different frequencies or different propagation directions. This type of wave is classified as a transverse wave (field disturbance at each occurring location is shown by a vector quantity perpendicular to the propagation direction) and longitudinal wave (here, those vector quantities are exactly aligned with the propagation direction). Mechanical waves comprise both longitudinal waves and transverse waves. Sound waves in fluid mediums are strictly longitudinal, while electromagnetic plane waves are transverse waves.
3) Give some examples of a wave.
- Waves on the surface of water bodies.
- Oscillations in a guitar string.
- Electromagnetic waves (microwaves, light waves, radio waves).
- Seismic S-wave.
- Synchronised crowd wave in a football field.
4) What are the two types of waves?
Longitudinal waves and transverse waves are the two types of waves.
5) What is meant by a longitudinal wave?
It is a type of mechanical wave in which the medium’s oscillation is parallel to the direction in which the wave moves, and the medium’s displacement is in the same direction as that of the wave’s propagation. Longitudinal waves are also known as compression or compressional waves because these waves generate rarefaction and compression when propagating through a medium. They are also called pressure waves as they cause a decrease and increase in pressure.
6) What is the longitudinal wave formula?
y(x,t) = y0cos[ω(t – x/c)]
Where
“y” = displacement of the point on the propagating sound wave
“x” = distance of the point covered from the source of the wave
“t” = time elapsed
y0 = amplitude of the oscillations
“c” = speed of the wave
“ω” = angular frequency of the wave
“x/c” = time ( wave needs to cover the distance “x”)
7) What are the main characteristics of a longitudinal wave?
The longitudinal wave’s main characteristics are wavelength, rarefaction, compression, period, frequency, and amplitude.
8) What is meant by compression?
In longitudinal waves, compression is a three-dimensional area in which the wave particles are nearest to each other.
9) What is meant by rarefaction?
In longitudinal waves, rarefaction is the region in which the wave particles are farthest from each other.
10) What is meant by wavelength?
The length between two adjacent points in a longitudinal wave is called wavelength. These adjacent points can be between two rarefactions or compressions.
11) What is meant by amplitude?
The maximum displacement of a vibrating particle from its resting position is known as amplitude. In longitudinal waves, the length from the equilibrium point in the propagation medium to rarefaction or compression is known as the amplitude.
12) What is meant by frequency and period?
The time needed by the wave to travel one wavelength is called the period.
The number of wavelengths per unit time (second) is called the frequency.
13) What is a sound wave?
A sound wave is an important example of a longitudinal wave. It is generated by the fast oscillation of the particles that move through an elastic medium. The sound produced by a tuning fork is a perfect example of sound waves existing in a longitudinal direction. In a sound wave, the amplitude is the distance between the pressure of the disturbed medium and the maximum pressure generated by the wave. The speed of sound relies on the composition, type, and the temperature of the propagation medium via which the sound travels.
14) What is meant by pressure waves?
Pressure waves (like a sound wave) are waves in which the moving disturbance is a change of pressure in a medium made of physical materials.
15) What is meant by transverse waves?
In classical mechanics, a transverse wave is a type of wave whose vibrations are perpendicular to the direction of the wave’s movement. This is totally different from the propagation of longitudinal waves, which propagates in the direction of their vibrations. Electromagnetic waves (microwaves, light waves, and radio waves) are an example of transverse waves.
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Practice Questions
1) What are the main types of waves?
2) What is meant by a mechanical wave?
3) What is the main difference between longitudinal waves and transverse waves?
4) What is meant by the medium of propagation?
5) What is the relationship between the speed of a longitudinal wave and its medium?
6) What is the principle behind the working of a tuning fork?
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