Sound

 

Sound is a form of energy that is produced by vibrations. When an object vibrates, it causes the surrounding air particles to vibrate and form sound waves. These waves travel through a medium and reach our ears, allowing us to hear.
Example:
A guitar string vibrates → air vibrates → sound reaches your ears.

Mediums of Sound Travel 

Sound needs a medium to travel. It cannot travel in a vacuum. The mediums are :

1. Solid – fastest
2. Liquid – medium
3. Gas – slowest

Reason: Particles in solids are closest together, making transmission easier.

 

Types of Sound Waves 

 Sound waves are longitudinal waves. This means the particles of the medium move back and forth in the same direction as the wave.

Compression shows particles are close together and Rarefaction shows particles are spread out.

 

Properties of Sound 

A. Loudness (Amplitude)

• Loudness depends on the amplitude of the vibration.

• Higher amplitude → louder sound

• Lower amplitude → softer sound

Unit: decibel (dB)

B. Pitch (Frequency)

• Pitch tells how high or low a sound is.

• It depends on the frequency of the sound wave.

Frequency: number of vibrations per second
Unit: Hertz (Hz)

• High frequency → high pitch (like a whistle)

• Low frequency → low pitch (like a drum)

 

C. Speed of Sound

Speed of sound depends on:

• Medium (solid > liquid > gas)

• Temperature (higher temperature → faster speed)

Average speed in air: 340 m/s

 

 D. Timbre (Quality of Sound)

• Timbre makes different sounds unique even if they have the same pitch and loudness.

• It depends on the waveform produced by different instruments.

Example:
A piano and a guitar playing the same note still sound different.

 

5. Reflection of Sound (Echo)

Sound can bounce off surfaces, especially hard surfaces.

• Echo: reflection of sound heard after a delay

• Delay happens when sound travels at least 17 meters before returning to your ear.

 

6. Absorption of Sound

Soft, porous materials can absorb sound, reducing echoes.

Examples:

• Carpets

• Curtains

• Foam panels

Used in: studios, cinemas, classrooms.

 

7. Applications of Sound

A. Sonar (Sound Navigation and Ranging)

• Uses ultrasonic waves to measure distance underwater.

B. Ultrasound

• Used in medical imaging to view internal organs.

C. Musical Instruments

• Produce sound by vibrating strings, air columns, or membranes.

   

  8. Human Hearing Range

• Humans can hear between 20 Hz to 20,000 Hz.

• Below 20 Hz → Infrasound

• Above 20,000 Hz → Ultrasound

        Animals such as bats and dolphins can hear ultrasound.

 

 Measuring Sea Depth Using Sound (SONAR)

SONAR (Sound Navigation and Ranging) is a technology that uses reflected sound waves to measure the distance to underwater objects or the ocean floor.

How It Works

1. A SONAR device sends a pulse of ultrasonic sound into the water.

2. The sound travels down until it hits the seafloor.

3. The sound wave is reflected back to the receiver on the ship.

4. The SONAR measures the time (t) taken for the sound to return.

5. Using the speed of sound in water, the depth is calculated.

Formula for Measuring Sea Depth

 

Formula for Measuring Sea Depth

$$\text{Depth} = \frac{1}{2} \times v \times t$$

Where:

• $v$ = speed of sound in water (approx 1500 m/s)

• $t$ = round-trip time (down and back)

Why divided by 2?

Because the sound travels twice:

• From the ship → to the seabed

• From the seabed → back to the ship

Example Problem

A SONAR system sends a sound pulse and receives the echo 4 seconds later.
Find the depth of the ocean.

$$\text{Depth} = \frac{1}{2} \times 1500 \times 4 = 3000 \text{ m}$$

So, the ocean is 3000 meters deep.