IGCSE 0625 · SOUND · 3.4

Sound

Sound as a longitudinal wave: how it travels, what sets loudness and pitch, how fast it moves in different materials, echoes, and the Extended ideas of ultrasound and sonar.

TOPIC 3.4: SOUND CORE CORE EXTENDED EXTENDED SOUND & HEARING A LONGITUDINAL WAVE Sound is made by vibrations and travels as a longitudinal wave of compressions and rarefactions. The particles vibrate along the direction of travel. Sound needs a medium, so it cannot travel through a vacuum. compression rarefaction travel LOUDNESS & PITCH Amplitude sets loudness; frequency sets pitch. quiet (small amplitude) loud (large amplitude) low pitch (low f) high pitch (high f) HEARING & ECHOES A healthy human hears about 20 Hz to 20 000 Hz. An echo is sound reflected from a hard surface. Measure the speed of sound from an echo: time the gap, then use v = 2d / t. source wall distance d v = 2d / t KEY FACTS Speed in air is roughly 330 to 340 m/s. Faster in liquids, fastest in solids. Sound cannot travel through a vacuum. v = 2d / t echo method SPEED IN DIFFERENT MATERIALS Closer, more tightly bound particles pass on the vibration faster, so sound travels: Gas (air) Liquid (water) Solid (steel) slow → fast as particles get closer together. In a vacuum there are no particles to carry the vibration, so no sound is heard. ULTRASOUND EXTENDED Ultrasound is sound above 20 000 Hz, beyond human hearing. It is sent as pulses and the echoes are timed. Prenatal and medical scanning. Cleaning delicate items and teeth. Detecting flaws and cracks in metal. transducer SONAR: MEASURING DEPTH EXTENDED A ship sends an ultrasound pulse to the seabed and times the echo. The pulse travels the depth twice. d = v t / 2 d = depth, t = echo time sea surface seabed depth d
TOPIC 3.4: SOUND CORE CORE EXTENDED EXTENDED SOUND & HEARING A LONGITUDINAL WAVE Sound is made by vibrations and travels as a longitudinal wave of compressions and rarefactions. The particles vibrate along the direction of travel. Sound needs a medium, so it cannot travel through a vacuum. compression rarefaction travel LOUDNESS & PITCH Amplitude sets loudness; frequency sets pitch. quiet (small amplitude) loud (large amplitude) low pitch (low f) high pitch (high f) HEARING & ECHOES A healthy human hears about 20 Hz to 20 000 Hz. An echo is sound reflected from a hard surface. Measure the speed of sound from an echo: time the gap, then use v = 2d / t. source wall distance d v = 2d / t KEY FACTS Speed in air is roughly 330 to 340 m/s. Faster in liquids, fastest in solids. Sound cannot travel through a vacuum. v = 2d / t echo method SPEED IN DIFFERENT MATERIALS Closer, more tightly bound particles pass on the vibration faster, so sound travels: Gas (air) Liquid (water) Solid (steel) slow → fast as particles get closer together. In a vacuum there are no particles to carry the vibration, so no sound is heard. ULTRASOUND EXTENDED Ultrasound is sound above 20 000 Hz, beyond human hearing. It is sent as pulses and the echoes are timed. Prenatal and medical scanning. Cleaning delicate items and teeth. Detecting flaws and cracks in metal. transducer SONAR: MEASURING DEPTH EXTENDED A ship sends an ultrasound pulse to the seabed and times the echo. The pulse travels the depth twice. d = v t / 2 d = depth, t = echo time sea surface seabed depth d
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