ICSE Class 10 Physics: Sound — Wave Properties & Notes 2026

Nature of Sound Waves

• Sound is a longitudinal mechanical wave; needs material medium
• Compressions and rarefactions; how pressure oscillates
• Cannot travel in vacuum — bell jar experiment

Wave Characteristics

• Frequency (f), wavelength (λ), amplitude (A), time period (T)
• Speed v = fλ; v in air at 0°C = 332 m/s, increases ~0.6 m/s per °C
• Relationship T = 1/f; Hz as SI unit

Speed of Sound in Different Media

• Speed: solids > liquids > gases; molecular spacing explanation
• Effect of temperature on speed in gases: v ∝ √T
• Practical: thunder arrives after lightning; calculate distance

Reflection of Sound — Echo and Reverberation

• Echo: reflected sound heard distinctly; minimum distance = 17 m (at 20°C)
• Reverberation: persistence of sound due to multiple reflections
• Acoustics of auditoriums; sound-absorbing materials

Resonance

• Natural frequency: every object vibrates at its own frequency
• Resonance occurs when driving frequency = natural frequency; amplitude increases dramatically
• Examples: Helmholtz resonator, tuning forks, Barton's pendulums

Doppler Effect

• Apparent change in frequency due to relative motion between source and observer
• Source moving towards observer: higher apparent frequency (higher pitch)
• Applications: SONAR, radar speed guns, ultrasound in medicine

Loudness, Pitch and Quality

• Loudness ∝ amplitude²; unit decibel (dB)
• Pitch determined by frequency; higher frequency = higher pitch
• Quality (timbre) determined by waveform shape; distinguishes instruments at same pitch