 # Propagation of Sound

## •    A medium is necessary for the propagation of sound. •    Sound can travel through solid, liquids and gases. •    Sound cannot travel in vacuum.•    Sound travels fastest in solid medium and slowest in gaseous medium. •    Sound travels faster in water than in air. •    Sound waves travel in air in the form of longitudinal waves. It appears as if the compressions and rarefactions are moving away towards the other end. •    The characteristics of a sound wave are its wavelength, frequency, amplitude and speed. •    Wavelength of a sound wave is the distance between two consecutive compressions or two consecutive rarefactions. •    SI unit of wavelength is metre. It is denoted by (λ). •    Wavelength basically represents the length of one wave. •    Wavelength determines the loudness or softness of sound. •    Speed of sound is the distance travelled by a point on a wave (such as compression or rarefaction) per unit time. •    The speed of the sound in a medium remains almost the same for all the frequencies, provided the physical conditions (state of the medium and temperature) don’t change. •    The speed of sound increases with increase in temperature of any medium. The speed of sound decreases from solid to gaseous medium. It is maximum in solids and minimum in gases. •    Light travels faster than sound. This is why we see the lighting first and hear the sound of thunder a little later even though they occur simultaneously. •    Sound waves get reflected at the surface of solids or liquids. But, an obstacle of large size having a rough or polished surface is required for reflection of sound. •    Rolling thunder is basically due to successive reflections from the clouds. The echo of sound is produced due to reflection of sound. •    Good absorbers of sound are materials like clothes, papers, thermocol, coating of plaster of Paris, carpets, curtains, furniture, wood, fiber board etc.

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• Q1

A sensation depending upon frequency is known as

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pitch.

##### Explanation:
Frequency determines the pitch and shrillness of a sound produced. If the frequency of vibration is higher, the sound produced is shrill and is of high pitch. If the frequency of vibration is lower, the sound produced is dull and is of low pitch. Pitch is a sensation, which depends upon the frequency of sound.
• Q2

Frequency is measured in

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hertz.

##### Explanation:
The number of to and fro movements or the number of oscillations per second is called the frequency of oscillation. Frequency is expressed in 'hertz' which is denoted by the symbol Hz, according to the International System of Units(SI) which is accepted uniformly worldwide for general purpose and is in scientific context.
• Q3

The number of oscillations per second is called the

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frequency.

##### Explanation:
Frequency means the number of times a thing happens or appears. In sound, the number of times, oscillations take place in a given time is 'frequency'. Frequency is defined as the number of oscillations per unit time.
• Q4

If a pendulum produces 50 oscillations in 5 seconds, its frequency is

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10 Hz

##### Explanation:

Frequency is the number of oscillations in 1 second.

Number of oscillations made by the pendulum in 5 sec = 50

Number of oscillation made by the pendulum in 1 sec = 50 / 5 = 10

So, 10 oscillations are made by the pendulum in 1 second, i.e., its frequency = 10 Hz.