Sound Flashcards – Cambridge IGCSE (9–1) Physics 0972 (Extended) (2026–2028)

What produces sound?

A vibrating source.

How does a sound disturbance propagate through a medium?

The source causes particles in the surrounding medium to vibrate, passing the disturbance through the medium.

Why can sound not travel through a vacuum?

Sound needs a material medium to travel.

What makes a sound wave longitudinal?

Particles vibrate back and forth parallel to the direction the wave travels.

In a sound wave, how do compressions and rarefactions differ?

In compressions, particles are closer together; in rarefactions, they are farther apart.

What does a sound wave transfer through a medium, and does the medium as a whole travel with it?

It transfers energy without the medium as a whole travelling with the wave.

What does the amplitude of a sound wave measure?

The size of its vibrations.

How does a sound wave’s amplitude affect its perceived loudness?

Greater amplitude sounds louder; smaller amplitude sounds quieter.

Which property of a sound wave determines its pitch rather than its loudness?

Frequency.

What is the frequency of a sound wave, and what unit is it measured in?

The number of vibrations per second, measured in hertz (Hz).

How does sound frequency affect pitch?

A higher frequency produces a higher pitch; a lower frequency produces a lower pitch.

Is a sound’s pitch the same as its loudness?

No. Pitch and loudness are distinct.

What is the approximate range of sound frequencies audible to humans?

$20\,\text{Hz}$ to $20{,}000\,\text{Hz}$.

What is ultrasound?

Sound with a frequency above $20\,\text{kHz}$ ($20{,}000\,\text{Hz}$), beyond the approximate upper limit of human hearing.

What is the approximate speed of sound in air?

$330–350\ \mathrm{m/s}$

How is speed calculated from distance travelled and time taken?

$v = \frac{d}{t}$

A distant source produces a sound and a visible signal at the same time. What distance and time are measured to estimate the speed of sound?

Measure the distance from the source to the observer and the time between seeing the signal and hearing the sound.

Why can the time between seeing a distant signal and hearing its sound be treated as the sound travel time?

The light travel time is negligible compared with the sound travel time.

How can repeated measurements improve an estimate of the speed of sound in air?

Repeat the measurement and average the results.

What is an echo?

Sound heard after sound waves reflect from a surface.

Why does an echo reach a listener after the direct sound?

The reflected sound travels back to the listener after reflecting from a surface.