Revision: Sound Physics HSC Science (General) 11th Standard Maharashtra State Board

The sound of frequency below 20 Hz is called infrasonic.

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).

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

A pattern which moves through material medium by repeated vibration of the particles of the medium about their mean position without the actual movement of matter is called a wave.

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

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

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

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.

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 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 required to complete one vibration by a particle, i.e., the time taken by a particle of a medium to complete one vibration, is called period.

Wavelength (λ): The distance between two successive particles which are in the same state of vibration is called the wavelength of the wave. SI unit is (m).

Amplitude (A): The largest displacement of a particle of a medium through which the wave is propagating, from its rest position, is called the amplitude of that wave. SI unit is (m).

The magnitude of maximum displacement of the constituent particle of the medium from their equilibrium position, i.e., the largest displacement of a particle of a medium through which the wave is propagating from its rest position, is called amplitude.

Waves in which a disturbance created at one place travels to distant points and keeps travelling unless stopped by an external force are known as travelling or progressive waves.

The distance covered by a wave per unit time is called velocity.

The state of oscillation of a particle is called its phase.

The number of vibrations performed by a particle per unit time is called frequency.

The minimum distance between two points having the same phase, or the distance between two consecutive crests or troughs in a wave, is called wavelength.

OR

The distance between two successive particles which are in the same state of vibration is called wavelength.

A wave in which particles of the medium vibrate in a direction perpendicular to the direction of propagation of the wave is called a transverse wave.

A wave in which particles of the medium vibrate in a direction parallel to the direction of propagation of the wave is called a longitudinal wave.

The expression (kx − ωt + ϕ) which represents the position x and time t dependent term in the wave equation is called the argument of the wave and phase of the particle at x at time t.

When two waves of the same frequency, wavelength and velocity move in the same direction, on superposition, they result in interference.

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 characteristic of sound that refers to the sharpness or shrillness of sound, determined by the frequency of the sound wave, is called pitch.

The unique quality that distinguishes one sound from another even if they have the same pitch and loudness is called timbre.

The apparent change in frequency of sound heard by a listener due to relative motion between the source and the listener is called the Doppler effect.

The apparent change in the frequency of sound heard by a listener, due to relative motion between the source of sound and the listener is called Doppler effect in sound.

When the source and the observer are in relative motion with respect to each other and to the medium in which sound propagates, the frequency of the sound wave observed is different from the frequency of the source. This phenomenon is called Doppler Effect.

A wave travelling along the positive X-axis is expressed as:

\[y(x,t)=a\sin(kx-\omega t+\phi)\]

When two or more pulses overlap, the resultant displacement is the algebraic sum of the displacements due to each pulse.

• Double Periodicity: A wave is periodic in both time and space.
• Phase indicates the position of a particle in its oscillation cycle.
• Frequency is measured in vibrations per second (Hz).
• Wavelength can also be understood as the distance between two successive particles in the same state of vibration.
• Amplitude is always measured from the rest (equilibrium) position of the particle.