Sound Class 10 ICSE — Selina Chapter 7
This Sound Class 10 ICSE chapter from Selina Physics Book 7 explains how sound is produced, how it travels as a longitudinal wave, and the three characteristics — loudness, pitch and quality — that let us tell one sound from another. You will learn the wave terms amplitude, time period, frequency and wavelength, the decibel unit of loudness, and how pitch is controlled in stringed, wind and membrane instruments.
Download Sound Class 10 ICSE Physics Chapter 7 PDF
Download the Sound Class 10 ICSE Physics chapter PDF from the Selina Concise textbook to revise offline or print for practice. It is the full chapter as printed in the book — 15 pages, 3 sections, 33 questions.
What is inside Chapter 7
15 pages · 3 sections · 1 worked examples · 33 exercise questions
| Section | Title |
|---|---|
| 1 | In this chapter you will learn to |
| 2 | KNOWING CONCEPTS |
| 3 | INTRODUCTION |
- TEST YOURSELF: 0 questions
- A. Objective Questions :: 4 questions
- B. Short/Long Answer Questions :: 29 questions
1 In this chapter you will learn to
This opening section states the goals of the chapter. The author tells you exactly what you should be able to do when you finish. Each goal maps to a later section, so the list works as a checklist while you revise.
The five learning goals are:
- Relate pitch and frequency.
- Understand pitch and frequency in the working of wind, membrane and string instruments.
- Explain what a monotone is.
- Relate loudness and amplitude.
- State the unit of loudness in decibels.
The chapter also includes a hands-on design task. You will build a musical toy that applies these ideas about pitch, loudness, frequency and amplitude. That activity is the practical payoff of the whole chapter.
2 KNOWING CONCEPTS
This short section lists the five concepts the chapter builds on. Skim it first to test your recall before reading the detail.
- Pitch and frequency.
- Pitch and frequency in the working of wind, membrane and string instruments.
- Monotone.
- Loudness and amplitude.
- The unit of loudness — decibels.
If you cannot define a term on this list yet, the corresponding section of the chapter will fill the gap.
3 INTRODUCTION
Sound is a form of energy that produces a sensation of hearing. It is produced when a body vibrates. Every source of sound — a string, a drum, a tuning fork — is a vibrating body.
Sound needs a medium to travel. It cannot travel in vacuum. This is why two people cannot hear each other on the moon, where there is no atmosphere. Sound can travel through solids, liquids and gases.
Speed depends on the medium. In iron, sound travels at about 5000 m/s. In water, it is about 1500 m/s. In air, it is about 330 m/s. Sound moves fastest in solids and slowest in gases.
When a body vibrates, the particles of the medium also vibrate. Kinetic energy changes into potential energy and back, which is why sound carries energy.
Propagation of sound in air
Take a vertical metal strip fixed at its lower end. Push its upper end to one side and release it. The strip vibrates, moving alternately right and left.
As the strip moves right, it pushes the air layer in front of it. The air particles come closer together, forming a compressed region called a compression. When the strip returns and moves left, it pulls the air layer, creating a low-pressure region called a rarefaction.
One complete to-and-fro motion forms one compression and one rarefaction. Together they make one wave. The disturbance moves forward, but the air particles do not travel with it. They vibrate about their mean positions and pass energy along.
This wave, in which particles vibrate in the direction of propagation, is a longitudinal wave. Sound travels through air as longitudinal waves. Such waves can form in solids, liquids and gases.
Terms related to a wave
This section defines four terms you need for the rest of the chapter.
Amplitude is the maximum displacement of a particle from its mean position. It is denoted by a and measured in metres. Time period is the time a particle takes to complete one vibration. It is denoted by T and measured in seconds.
Frequency is the number of vibrations a particle completes in one second. It is denoted by f. Its unit is second⁻¹ or hertz (Hz). Wavelength is the distance the wave travels in one time period. It is denoted by λ and measured in metres.
Frequency and time period are linked by:
f = \frac{1}{T}
Frequency is a property of the source. It does not depend on amplitude or on the medium. Wavelength, however, does depend on the medium. In a longitudinal wave, the distance between two consecutive compressions — or two consecutive rarefactions — equals one wavelength.
Edge case to remember: if a particle completes one vibration in 0.25 s, its frequency is 4 Hz, since \frac{1}{0.25} = 4. The frequency stays 4 Hz whether the wave moves through air, water or iron; only wavelength changes.
Representation of a wave
Two graphs represent a wave. Each shows different information.
The displacement-time graph tracks one particle over time. From it you read amplitude and time period. For example, if the graph shows amplitude 2 cm and time period 4 s, then frequency is 0.25 Hz.
The displacement-distance graph shows all particles at one instant. From it you read amplitude and wavelength. For example, a graph with amplitude 2 cm and wavelength 2 m describes the wave at that moment.
Three notes complete this section. Positive displacement on the Y axis means particles move in the direction of propagation; negative means the opposite. If particles vibrate at right angles to propagation, the wave is transverse. Sound waves in strings are transverse.
Characteristics of sound
A sound wave is defined by its amplitude and frequency. From these come three characteristics that let us tell sounds apart.
Loudness distinguishes a loud sound from a faint one at the same frequency and wave form. Pitch (or shrillness) separates a shrill sound from a flat one. Quality (or timbre or wave form) distinguishes two sounds of the same pitch and loudness.
Loudness grows with the square of amplitude:
L \propto a^2
Doubling the amplitude makes loudness four times greater. Tripling it makes loudness nine times greater.
Worked pattern: two waves have amplitudes 2 cm and 5 cm. Their loudness ratio is:
\frac{L_A}{L_B} = \frac{(2\ \text{cm})^2}{(5\ \text{cm})^2} = \frac{4}{25}
The 5 cm wave is louder, because loudness depends on the square of amplitude.
Four factors affect loudness: the amplitude of the wave, the distance of the source, the surface area of the vibrating body, and the sensitivity of the listener’s ear.
| Characteristic | Determining factor |
|---|---|
| Loudness | Amplitude |
| Pitch | Frequency |
| Quality | Wave form |
Common mistake: students confuse loudness with pitch. Loudness depends on amplitude. Pitch depends on frequency. A high-frequency sound can still be soft if its amplitude is small.
Unit of loudness — decibel (dB)
Loudness is measured on the decibel scale. One decibel is one-tenth of a bel, named after Alexander Graham Bell, the inventor of the telephone.
The zero level is the minimum audible sound at a frequency of 1 kHz. It is the reference level. When loudness increases ten times, the level rises to 10 dB. A hundredfold increase gives 20 dB, and a thousandfold gives 30 dB.
| Object | Level (dB) |
|---|---|
| Minimum audible | 0 |
| Whisper | 30 |
| Normal conversation | 50 |
| Vehicle | 80 |
| Police car siren | 120 |
| Rocket take off | 140 |
The safe limit for hearing is 0 to 80 dB. Levels from 10 to 30 dB feel soothing. Constant exposure above 120 dB can cause headache and permanent ear damage. Such sound is called noise.
One distinction matters. Intensity can be measured, but loudness cannot. Intensity does not depend on the listener’s sensitivity. Loudness does.
Pitch
Pitch is the characteristic that separates a shrill sound from a flat one. It depends on the number of vibrations per second — that is, on frequency. Higher frequency means higher pitch.
Examples from everyday life make this clear. A crying baby’s sound is shriller than an adult’s. A female voice is shriller than a male voice. On a tape recorder, bass means low pitch and treble means high pitch.
On a displacement-time graph, more waves in the same time means a smaller time period. That means higher frequency, and therefore higher pitch.
Ways of changing the pitch in different musical instruments
Each family of instruments controls pitch differently.
In stringed instruments — piano, violin, guitar — pitch depends on tension and thickness. A string under higher tension gives a higher note. A thinner string does too. Plucking closer to a fixed end also raises pitch.
In wind instruments — flute, clarinet, shehnai — pitch depends on the length of the vibrating air column. Closing holes lengthens the column and lowers pitch. Opening holes shortens it and raises pitch.
In membrane instruments — dholak, tabla, drum — pitch depends on the size and tension of the membrane. A tighter and smaller membrane gives a higher pitch.
Two activities in the chapter demonstrate the air-column idea. As water rises in a pitcher, the air column shortens and the sound becomes shriller. The same happens in a test tube as you add water.
Monotone
A monotone is a sound of a single frequency. The tuning fork is the only common source that produces such a sound.
A tuning fork is a U-shaped metallic piece with a stem and two prongs. Striking a prong with a rubber pad sets it vibrating at its own frequency, which is marked on the fork.
Common tuning fork frequencies are 256, 288, 320, 384, 480 and 512 s⁻¹. The wave form of a monotone is a clean single-frequency wave.
Quality (or timbre or wave form)
Quality is the characteristic that distinguishes two sounds of the same pitch and same loudness. It is also called timbre or wave form.
Every instrument or human voice carries, in small amplitudes, extra waves whose frequencies are integer multiples of the source frequency. These extra waves differ between sources, so each has a distinctive wave form.
This is why you recognise a person’s voice on the telephone without seeing them. It is why you can tell a piano from a flute even when both play the same note at the same loudness. A piano note contains many extra notes, while a flute note contains few.
Making a musical toy
The chapter ends with a hands-on build. You make a shoe box guitar from a shoe box, a cardboard tube, and five or six rubber bands.
You cut a hole in the box for the tube, then stretch the rubber bands across the box. Plucking the bands produces a twanging sound like a guitar.
This toy ties the chapter together. Plucking harder increases amplitude and therefore loudness. Using tighter or thinner bands changes pitch.
What to practise from Sound Class 10 ICSE
The chapter gives you four practice blocks. Each tests a different skill.
- TEST YOURSELF — a self-test covering the whole chapter.
- A. Objective Questions — 4 questions testing true or false, fill in the blanks, matching, and selecting the correct alternative.
- B. Short/Long Answer Questions — 29 questions on definitions, the three characteristics, and pitch control in instruments.
- C. Numericals — 2 questions on loudness ratios and frequency ratios.
The objective items test definitions: amplitude, frequency, time period, decibel. The short and long answers test the three characteristics and how instruments change pitch. The numericals test the square law for loudness and the pitch relation for frequency.
One common mistake appears often in true-or-false items. The statement that the distance from one compression to the nearest rarefaction is called wavelength is false. That distance is half a wavelength. One full wavelength is the distance between two consecutive compressions.
For more practice, you can explore other chapters in the Class 10 ICSE Physics book collection on this site.
Sound Class 10 ICSE frequently asked questions
What is the difference between loudness and pitch in sound class 10 icse?
Loudness is the characteristic that distinguishes a loud sound from a faint one. It depends on the amplitude of the wave. Pitch is the characteristic that distinguishes a shrill sound from a flat one. It depends on frequency. A wave can be loud and low-pitched, or soft and high-pitched, because the two characteristics depend on different factors.
Why does a tuning fork produce a monotone in Class 10 ICSE Physics?
A tuning fork vibrates at a single frequency, so it produces a sound of a single frequency. That sound is called a monotone. Most instruments produce many frequencies at once, which is why their wave forms are complex.
How is loudness related to the amplitude of a wave in this Sound ICSE chapter?
Loudness is directly proportional to the square of amplitude, written L \propto a^2. Doubling the amplitude makes the sound four times louder. Tripling it makes the sound nine times louder.
Why can two people not hear each other on the moon in this ICSE chapter?
Sound needs a medium to travel. The moon has no atmosphere, so there is no air to carry sound waves. With no medium, sound cannot propagate, and no sound reaches the listener’s ear.
What is the safe limit of sound level in decibels for hearing in Class 10 ICSE?
The safe limit is 0 to 80 dB. Levels from 10 to 30 dB feel soothing. Constant exposure above 120 dB can cause headache and permanent ear damage. Sound above that level is called noise. For the official syllabus details, check the CISCE website.
You can also browse the full set of ICSE Class 10 books for other subjects and chapters.
Reference: ICSE Class 10 Physics textbook material, chapter 7: Sound — CISCE-aligned.