Sound
Introduction
Sound is a form of mechanical energy that propagates as longitudinal waves through a material medium. In ICSE Class 10 Physics, you study wave characteristics, types of vibrations, resonance, and the three characteristics of sound.
Wave Characteristics
| Term | Symbol | Definition | Unit |
|---|---|---|---|
| Amplitude | A | Maximum displacement from mean position | m |
| Wavelength | λ | Distance between two consecutive crests/troughs | m |
| Frequency | f or ν | Number of oscillations per second | Hz |
| Time period | T | Time for one complete oscillation | s |
| Velocity | v | Speed of wave propagation | m/s |
Wave Equation
v = f × λ
Types of Vibrations
Free (Natural) Vibrations
When a body is set into vibration and allowed to vibrate freely, it vibrates at its natural frequency.
Damped Vibrations
Vibrations whose amplitude decreases with time due to resistive forces (air resistance, friction).
Forced Vibrations
When a body is made to vibrate at a frequency different from its natural frequency due to an external periodic force.
Resonance
Resonance occurs when the frequency of the externally applied periodic force equals the natural frequency of the body, resulting in a large amplitude of vibration.
Examples of Resonance
- A singer breaking a glass by matching its natural frequency.
- A swing pushed at the correct moment goes higher and higher.
- Soldiers marching in step can cause a bridge to collapse (break step when crossing a bridge).
Advantages and Disadvantages
| Advantages | Disadvantages |
|---|---|
| Tuning of radio/TV circuits | Can cause structural damage |
| Musical instruments (sound amplification) | Can shatter glass |
| Magnetic Resonance Imaging (MRI) | Unwanted vibrations in machines |
Characteristics of Sound
1. Loudness
- Depends on amplitude of the sound wave.
- Higher amplitude → louder sound.
- Measured in decibels (dB) .
2. Pitch (Shrillness)
- Depends on frequency of the sound wave.
- Higher frequency → higher pitch.
- Women have a higher-pitched voice than men.
3. Quality (Timbre)
- Depends on the waveform.
- Helps distinguish between sounds of same loudness and pitch from different sources (e.g., a piano vs a violin).
Comparison: Sound Waves vs Light Waves
| Property | Sound Waves | Light Waves |
|---|---|---|
| Nature | Mechanical, longitudinal | Electromagnetic, transverse |
| Medium required | Yes (material medium) | No (can travel in vacuum) |
| Speed in air | ~340 m/s | 3 × 10⁸ m/s |
| Speed in water | ~1500 m/s | 2.25 × 10⁸ m/s |
Common Mistakes and Fixes
| Mistake | Fix |
|---|---|
| Confusing loudness with pitch | Loudness ∝ amplitude²; Pitch ∝ frequency |
| Thinking sound can travel in a vacuum | Sound needs a material medium |
| Confusing free and forced vibrations | Free: natural frequency; Forced: external frequency |
| Applying v = fλ incorrectly | v is velocity of sound in the medium, not the source's speed |
ICSE Exam Focus
This chapter carries 4–6 marks. Key topics: wave equation numericals, resonance, characteristics of sound, types of vibrations.
Marks Blueprint: Wave characteristics — 2 marks, Resonance — 2 marks, Loudness/Pitch/Quality — 2 marks.
Self-Test Questions
-
A sound wave has a frequency of 440 Hz and a speed of 330 m/s. Find its wavelength.
-
Distinguish between free, damped, and forced vibrations with examples.
-
What is resonance? Give two examples of resonance in everyday life.
-
On what factors does the loudness of sound depend? How is loudness different from pitch?
-
Why can sound not travel through a vacuum?
-
A wave completes 200 oscillations in 5 seconds. If its speed is 340 m/s, find the wavelength.
