Topic 6 of 8Cambridge O Levels

Waves & Sound

How sound travels and why you hear the azaan from far away

A wave transfers energy from one place to another without transferring matter.

Types of Waves:

Transverse waves: Particles vibrate perpendicular to the direction of travel (e.g., light, water waves)

Longitudinal waves: Particles vibrate parallel to the direction of travel (e.g., sound waves, compression springs)

Wave Properties:

Wavelength (λ): Distance between two identical points on consecutive waves

Frequency (f): Number of waves per second (in Hertz, Hz)

Amplitude: Maximum displacement from rest position

Speed: v = fλ (wave speed = frequency × wavelength)

Sound Waves:

Sound is a longitudinal wave that needs a medium (solid, liquid, or gas) to travel

Speed of sound in air ≈ 340 m/s

Sound travels faster in solids than gases (particles are closer)

Cannot travel in a vacuum (space is silent!)

Echoes: Sound reflecting off surfaces. Used in sonar and ultrasound.

Distance = (speed × time) / 2 (divide by 2 because sound travels there and back)

Pitch & Loudness:

Higher frequency = higher pitch

Greater amplitude = louder sound

Key Points to Remember

1Wave speed = frequency × wavelength (v = fλ)
2Sound is a longitudinal wave, needs a medium
3Speed of sound in air ≈ 340 m/s
4Echoes: distance = (speed × time) / 2

Pakistan Example

The Mosque Loudspeaker & the Azaan

When the azaan plays from a mosque, sound waves travel through the air at about 340 m/s. If you hear the azaan 2 seconds after it starts from a mosque, you're about 680 metres away (340 × 2 = 680m). In cities like Lahore, you might hear the same azaan from multiple mosques at slightly different times — the delay depends on your distance from each mosque. The loudspeaker increases the amplitude of the sound waves, making the azaan louder without changing its pitch.

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