Notes on Sound and its Properties | Grade 9 > Science > Sound | KULLABS.COM

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A sound is a form of energy which gives a sensation of hearing. The sound is produced due to the vibration of the body. Sound travels through a medium by means of waves set up in the medium. The following are the characteristics of sound;

• It is produced due to the vibration of the body.
• It needs a medium for propagation. It cannot travel through a vacuum.
• Its speed is different in a different medium. Its velocity is the highest in solids and slowest in gases.
• Sound travels from one place to another in the form of a longitudinal wave.
• Sound follow reflection and refraction phenomenon.

#### Relation between frequency and time period

By the definition of frequency,

∴ f vibrates are completed in one second.

∴ 1 vibration is completed in 1/f second.

But, time to complete one vibration is its time period (T)

∴ T = 1/f

#### Factors affecting velocity of sound in gases

Temperature: The velocity of sound is directly proportional to square root of the absolute temperature of the gas. Thus, higher the temperature, higher the velocity of sound.

∴ Velocity of sound ∝ Density: The velocity of sound in a gas is inversely proportional to the square root of the density of the gas.

∴ Velocity of sound ∝ Humidity: As the density of water vapour is less than that of dry air, the density of moist air is lesser than that of dry air. Sound travels faster in moist air than in dry air as the velocity of sound in a gas is inversely varies inversely to square root of the density of the gas.

The direction of wind: Direction of wind also affect the velocity of sound. The velocity of sound is higher in the direction of wind and slower in the opposite direction of the wind.

• The velocity of sound is directly proportional to square root of the absolute temperature of the gas.
• The velocity of sound in gas is inversely proportional to the square root of the density of the gas.
• Sound travels faster in moist air than in dry air as the velocity of sound in gas is inversely varies inversely to square root of density of the gas.
• Sound transmits from one place to another in the form of a longitudinal wave.
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### Very Short Questions

Velocity of sound in gas depends on the following factors,

• Density of gas
• Temperature of gas
• Humidity of gas
• Direction of wind

Sound waves are mechanical waves so they need material medium to carry energy from the sources. Hence, sound wave can not travel in vacuum.

A sensation caused in the ear by the vibration of the air and any other medium is called sound. It is a form of energy. The sound is produced due to the vibration of the molecular medium (i.e. objects).

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• ### The form of energy that is produced due to the vibration of the body is known as

Light energy
Nuclear energy
Sound energy
Wind energy

Vacuum
Liquid
Air
Solid

Solids
Gas
Soil
Liquid

Liquid
Gases
Solid
Rock
• ### Sound transmits from one place to another in the form of a

None of them
Longitudinal wave
Both of them
Transverse wave
• ### When the density of air increases then the velocity of sound in air

Decreases
Increases
Remains uneffected
Becomes 0
• ### When the temperature of gas increases then the velocity of sound in gas

Decreases
Increases
Remains uneffected
Becomes 0
• ### The velocity of the sound is higher if the direction of wind is

In upward direction
In downward direction
In the same direction
In opposite direction
• ### The velocity of the sound is lesser if the direction of the wind is

In the opposite direction
In equivalent direction
In the similar direction
In the same direction
• ### Sound travels faster in

Moist air
Air with less density
Dry air
Cool air