Revision: Sound >> Sound Physics (English Medium) ICSE Class 10 CISCE

The wavelength of a sound wave is the spatial distance over which the wave's shape repeats. Because sound is a longitudinal wave, it is specifically defined as the distance between two consecutive points in the same phase of vibration.

The process by which bats and dolphins detect the presence of an obstacle by hearing the echo of the sound produced by them is called sound ranging. 

The time period of a particle executing S.H.M. is the time taken to complete one cycle and is denoted by T.

The linear distance between the two consecutive particles of a vibrating medium in the same phase is called its wavelength. It is denoted by the Greek letter lambda (λ).

Our ears are sensitive only to a limited range of frequencies from 20 Hz to 20,000 Hz, which is called the audible range of frequency.

The sound of frequency above 20,000 Hz is called ultrasonic.

The sound of frequency below 20 Hz is called infrasonic.

When a sound wave travels in a medium, the maximum displacement of the particle of the medium on either side of its mean position, is called the amplitude (a) of the wave.

The time taken by the particle of the medium to complete its one vibration, is called the time period (T) of the wave.

The number of vibrations made by the particle of the medium in one second, is called the frequency (j) of the wave.

The distance travelled by a wave in one time period of vibration of the particle of the medium, is called the wavelength (λ).

The distance travelled by the wave in one second is called the wave velocity (V).

If the vibrations of medium particles are along the direction of propagation of the wave, thus forming compressions and rarefactions in the medium, the wave is called a longitudinal wave.

If the medium particles vibrate normal to the direction of propagation of the wave, forming crests and troughs, the wave is called a transverse wave.

The sound heard after reflection from a rigid obstacle (such as cliff, a hillside, a wall of a building, edge of a forest etc.), is called an echo.

The number of vibrations per second taken by a wave is called its frequency.

The maximum displacement of the particle of medium on either side of its mean position is called the amplitude of the wave. Its S.I. unit is a meter (m).

The number of vibrations made by a particle of the medium in one second is called the frequency of the waves. It is also defined as the number of waves passing through a point in one second. It's S.I. unit is hertz (Hz).

The return of a sound wave on striking a surface such as wall, metal sheet, plywood etc. back in the same medium is called the reflection of sound wave.

The distance travelled by a wave in one second is called its wave velocity. It's S.I. unit is metre per second (ms^-1).

The distance travelled by the wave in one time period of vibration of a particle of medium is called its wavelength. It's S.I. unit is metre (m).

The sound heard after reflection from a distant obstacle (such as a cliff, a hillside, wall of a building, edge of a forest, etc.) after the original sound has ceased, is called an echo.

The frequency of natural vibrations is called the natural frequency.

The amplitude of a particle executing S.H.M. is its maximum displacement on either side of the mean position.  A is the amplitude of the particle.

The periodic vibrations of a body in the absence of any external force on it, are called natural (or free) vibrations.

The time period of the natural vibrations is called its natural period.

The periodic vibrations of a body of decreasing amplitude in presence of a resistive force are called damped vibrations. 

The vibrations of a body which take place under the influence of an external periodic force acting on it, are called forced vibrations.

Resonance is a special case of forced vibrations. When the frequency of the externally applied periodic force on a body is equal to its natural frequency, the body readily begins to vibrate with an increased amplitude. This phenomenon is known as resonance.

The vibrations of large amplitude are called resonant vibrations.

The frequency of a particle executing S.H.M. is equal to the number of oscillations completed in one second. 

Timbre is the characteristic that distinguishes two sounds of the same loudness and pitch of two different instruments.

Loudness is the characteristic by virtue of which a loud sound can be distinguished from a faint one, both having the same pitch and quality.

The intensity of a sound wave at any point of the medium is measured as the amount of sound energy passing per second, normally through a unit area at that point. 

Intensity is defined as the amount of energy per unit of time perpendicular to the direction of propagation of the wave.

Pitch is that characteristic of sound by which an acute (or shrill) note can be distinguished from a grave (or flat) note of the same loudness and quality.

Quality (or timbre) of a sound is that characteristic which distinguishes the two sounds of the same loudness and same pitch, but emitted by two different instruments because of change in their wave forms.

The sound other than the musical sound is called noise.

or

It is a sound produced by an irregular succession of disturbances.

It is a pleasant, continuous and uniform sound produced by regular and periodic vibrations. 

v = \[\frac{\text{total distance travelled}}{\text{time interval}} = \frac{2d}{t}\] m s^-1

• Echoes are used in sound ranging and echo depth sounding by using ultrasonic waves.
• Ultrasonic waves (frequency above 20 kHz) can travel undeviated for long distances, can be confined to a narrow beam, and are not easily absorbed in a medium.
• Bats, dolphins, and fishermen use echoes of ultrasonic waves to detect obstacles, enemies, and shoals of fish; this process is called sound ranging.
• SONAR (sound navigation and ranging) uses echoes of ultrasonic waves to detect underwater obstacles and to find the distance and depth of the sea.

• Resonance is demonstrated when the frequency of forced vibrations becomes equal to the natural frequency of a body.
• In tuning forks of the same frequency, the vibrating fork produces forced vibrations in the other fork, which then vibrates under resonance with large amplitude.
• In pendulums, the pendulum having the same natural frequency as the vibrating pendulum comes into resonance and vibrates with maximum amplitude and in phase.
• Pendulums with different natural frequencies remain in forced vibration and vibrate with very small amplitude.
• In an air column, resonance occurs when the natural frequency of the column matches the tuning fork's frequency, producing a loud sound.

• Loudness of sound depends on the amplitude of the wave, and a loud sound corresponds to a wave of large amplitude.
• Intensity of a sound wave is the amount of sound energy passing per second, usually through a unit area, and its unit is watts per square metre² (W m⁻²).
• Loudness is subjective because it depends on the listener's ear sensitivity, whereas intensity is objective.
• Loudness depends on the square of the amplitude, the distance from the source, the surface area of the vibrating body, the density of the medium, and the presence of resonant bodies.
• Sound level is expressed in decibels (dB), and noise pollution is caused by undesirable loud and harsh sounds at levels above 120 dB.