 # AP Board Class 9 Physical Science Chapter 10 Sound

Andhra Pradesh Board Class 9 Physical Science Chapter 10 is an interesting chapter that deals with the topic of sound. In our daily lives, we hear different types of sounds from various sources and it is quite important to know a few things about them. Therefore, in this chapter, students will study about;

• Definition of Sound
• Nature of sound
• Sound production
• Propagation of sound
• Characteristics of sound

## What is Sound?

A sound is popularly defined as a form of mechanical energy which produces a sensation of hearing.

### Sound Production

Sound is usually produced when something or a body vibrates in quick succession. The vibrating body also causes the medium like water, air, etc. around it to vibrate.

### Propagation and Nature Of Sound

Sound usually travels in the form of a wave. Talking about the nature of sound, sound waves are longitudinal meaning the particles of the medium move to and fro along the direction of propagation of the wave. Sound waves cannot travel through a vacuum. In order for the sound to be transmitted, we require a definite medium be it solid, gas or liquid.

### Characteristics of Sound Wave

The characteristic of a sound wave mainly depends on four quantities, which are wavelength, frequency, amplitude, and wave speed.

1. Wavelength is the distance between two consecutive rarefactions or compressions.
2. Amplitude is the maximum variation in density or pressure from the mean value.
3. Frequency is the total number of oscillations of the density of the medium at a place per unit time.
4. The speed of sound is the distance by which a point of on the wave (be it either rarefaction or compression) moves per unit time.

Students can view some of the important questions given below and learn about some of the additional chapter topics.

Question 1: Define Pitch and Loudness.

Answer: Pitch is a unique characteristic of sound which helps us differentiate between a shrill or a deep, low sound. Meanwhile, the loudness of sound is defined as the degree of sensation produced in the ear.

Question 2: What are infrasonic and ultrasonic sounds?

Answer: Sounds having a frequency less than 20Hz are known as infrasonic sounds. Similarly, sounds having a frequency higher than 20KHz are known as ultrasonic sounds.

Question 3: What is the audible limit for a human ear?

Answer: The audible limit for a human ear is 20 to 20,000 Hertz.

Question 4: Define the wavelength of a sound wave.

Answer: The distance between two consecutive compressions or two consecutive rarefaction is called the wavelength of a
sound wave.

Question 5: What is the time period of a sound wave?

Answer: “The time taken to complete one oscillation of the density of the medium is called the time period of the sound wave”. The time period of the sound wave is represented by the symbol (T) and its SI unit is second (s).

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