10th Class Physics Chapter 13 Notes | Get Now
10th Class Physics Chapter 13 Notes cover “Sound,” a chapter that explains how sound is produced, how it travels, and how the human ear detects it. This chapter also covers loudness, pitch, resonance, and the practical uses of ultrasonic waves.
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Students search for 10th Class Physics Chapter 13 Notes because the chapter combines conceptual definitions with numerical problems involving decibels and wave speed, both of which are heavily tested in board exams.
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This guide simplifies every major topic in Chapter 13 so students can revise quickly and confidently.
What Is Sound and How Is It Produced?
Sound is a form of energy produced due to the vibration of a body. Whenever sound is produced, the vibrations of the sounding body can be observed or felt.
Demonstrating Sound Production
The 10th Class Physics Chapter 13 Notes describe two simple experiments:
- Pan Experiment: Striking an upside-down pan with a spoon creates vibrations that can be felt by touch and observed using small paper pieces placed on the pan.
- Tuning Fork Experiment: A U-shaped tuning fork vibrates when struck against a rubber pad, and this vibration can be felt or observed by dipping its prongs in water, causing splashing.
Nature of Sound and Compressional Waves
Sound is produced due to vibration, and vibrating bodies produce compressional waves, also called sound waves.
Compression and Rarefaction
As a tuning fork’s prong moves, it creates two effects:
- Compression: When the prong moves forward, it compresses the layer of air in front of it, transferring pressure to the next layer.
- Rarefaction: When the prong moves backward, pressure on the adjacent layer decreases, creating a rarefaction that also moves outward.
This continuous series of compressions and rarefactions forms sound waves, which is why sound waves are classified as compressional (longitudinal) waves.
Sound Needs a Medium to Travel
An important concept in the 10th Class Physics Chapter 13 Notes is that sound cannot travel through a vacuum — it needs a material medium.
Proof Through Experiments
- Vacuum Bell Jar Experiment: An electric bell inside a jar becomes fainter as air is pumped out, proving that air is necessary for sound propagation.
- Sound Through Water: A bell rung underwater can be heard clearly through a stethoscope, proving sound travels through liquids.
- Sound Through Solids: Striking one end of a long railing lets a person hear two sounds — one through the solid railing and one through air — showing that sound travels faster through solids than through air.
How the Human Ear Detects Sound
The ear is the organ of hearing and has three main parts, a key topic in 10th Class Physics Chapter 13 Notes:
1. Outer Ear
The visible horn-like part that collects sound waves and directs them to the eardrum through an open canal.
2. Middle Ear
Contains three tiny bones — the hammer, anvil, and stirrup — which transfer vibrations from the eardrum to the oval window.
3. Inner Ear
Contains the cochlea, a snail-shaped structure filled with fluid. Hair-like structures inside respond to different vibration frequencies and send signals to the brain via auditory nerves, where they’re interpreted as sound.
Characteristics of Sound
There are five main characteristics of sound covered in this chapter:
- Loudness of sound
- Intensity of sound
- Pitch of sound
- Quality of sound
- Noise and music
Loudness of Sound
Loudness is the characteristic that distinguishes a loud sound from a faint one. It depends on:
- Amplitude: Larger amplitude produces louder sound
- Area of vibrating body: A larger vibrating surface produces louder sound
- Distance from the vibrating body: Sound gets fainter as distance increases
Intensity of Sound
Intensity is the sound energy flowing per second through a unit area held perpendicular to the direction of the sound wave. Its unit is watt per meter square (Wm⁻²).
- Intensity of faintest audible sound: 10⁻¹² Wm⁻²
- Intensity of loudest sound without pain: 1 Wm⁻²
Weber-Fechner’s Law and Sound Level
According to Weber-Fechner’s Law, loudness is directly proportional to the logarithm of intensity, not intensity itself. This gives us the sound level formula used throughout 10th Class Physics Chapter 13 Notes:
Sound Level = 10 log(I/I₀) dB
Where I₀ is the intensity of the faintest audible sound. The unit of sound level is the decibel (dB), where 1 bel = 10 dB.
Pitch of Sound
Pitch is the characteristic that distinguishes a shrill sound from a grave sound, and it depends on frequency. Higher frequency means higher pitch — this is why women and babies typically have higher-pitched voices than men.
Quality of Sound
Quality distinguishes two sounds of the same loudness and pitch from each other, based on their waveform. This is why a flute and a piano playing the same note still sound different.
Musical Sound vs Noise
- Musical Sound: Has a pleasing effect, with frequency and amplitude changing in a regular manner
- Noise: Has a jarring effect, with frequency and amplitude changing irregularly
Finding the Speed of Sound (Resonance Method)
The 10th Class Physics Chapter 13 Notes explain the laboratory method for measuring sound speed using resonance.
How Resonance Works
A vibrating tuning fork is held over a tube connected to a water reservoir. As the air column length changes, at a certain length, the sound becomes loudest — this is called resonance, where the air column’s frequency matches the tuning fork’s frequency.
The relationship is:
λ/4 = ℓ (at first resonance), so λ = 4ℓ
Since V = fλ, the speed of sound becomes:
V = 4fℓ
Where ℓ is the length of the air column at first resonance.
Audible Frequency Range and Ultrasonics
Audible Frequency Range
A human ear can hear sounds only within the frequency range of 20 Hz to 20,000 Hz. This range decreases with age — older people often cannot hear sounds above 15,000 Hz.
Ultrasonics
Sounds with frequency higher than 20,000 Hz, inaudible to humans, are called ultrasonics. This is a key topic tested through both definitions and applications in 10th Class Physics Chapter 13 Notes.
Uses of Ultrasonics:
- Medical field: Diagnosing diseases, detecting tumors, finding a baby’s sex and physical condition, removing blood clots
- Technical field: Detecting cracks in machinery, ships, and aeroplane parts
- Finding ocean depth: Using reflected ultrasonic pulses from the ocean bed
- Killing germs: High-intensity ultrasonic waves destroy bacteria in liquids
- Dental care: Used for teeth scaling to remove plaque
- Removing kidney stones: Ultrasonic waves break down stones without surgery
Important Formulas in Chapter 13
| Concept | Formula |
|---|---|
| Sound level | L = 10 log(I/I₀) dB |
| Speed of sound (resonance) | V = 4fℓ |
| Wave speed | V = fλ |
| Distance | Distance = velocity × time |
Solved Numerical Examples
Common numerical problems in 10th Class Physics Chapter 13 Notes include:
- Calculating sound level in decibels when intensity is given
- Finding the distance of a gun from a listener using time delay and speed of sound
- Calculating the speed of sound using resonance tube length and frequency
- Finding wavelength when frequency and speed of sound are known
Practicing these numericals regularly helps students handle both direct calculations and multi-step problems in exams.
Why This Chapter Matters for Exams
Sound connects closely to Chapter 12’s wave motion concepts, making it essential to understand both together. A complete set of 10th Class Physics Chapter 13 Notes helps students:
- Understand how sound characteristics like loudness and pitch differ conceptually
- Solve decibel-based numericals confidently using logarithms
- Answer questions about ultrasonics and their real-world applications accurately
FAQs
Q1: What is 10th Class Physics Chapter 13 about?
10th Class Physics Chapter 13 covers Sound, including how sound is produced, how it travels through different mediums, the structure of the human ear, characteristics of sound, resonance, and the applications of ultrasonic waves.
Q2: What is the formula for finding the speed of sound using resonance?
The speed of sound using the resonance method is V = 4fℓ, where f is the frequency of the tuning fork and ℓ is the length of the air column at the first position of resonance.
Q3: What is the audible frequency range for humans?
The human ear can hear sounds with frequencies between 20 Hz and 20,000 Hz. Sounds below or above this range are inaudible to humans, though some animals like dogs can hear higher frequencies.
Q4: Why are 10th Class Physics Chapter 13 Notes important for exams?
This chapter combines conceptual definitions with numerical problems involving decibels and resonance. Understanding formulas like sound level and V = 4fℓ helps students handle both theory and calculation-based exam questions.
Q5: What are ultrasonic waves used for?
Ultrasonic waves, with frequencies above 20,000 Hz, are used in medical diagnosis, detecting cracks in machinery, measuring ocean depth, killing germs, teeth scaling, and removing kidney stones without surgery.
Q6: Does sound travel through a vacuum?
No, sound cannot travel through a vacuum because it requires a material medium like air, water, or solids to propagate. This was demonstrated by the vacuum bell jar experiment, where sound faded as air was removed.