Edexcel iGCSE Physics -3.23 Sound Waves- Study Notes- New Syllabus

Sound Waves: Longitudinal Waves, Reflection and Refraction

Sound waves are a type of mechanical wave that require a medium, such as air, water, or solids, to travel. Sound waves are longitudinal waves and can undergo reflection and refraction, just like light waves.

Sound Waves as Longitudinal Waves

A longitudinal wave is a wave in which the vibrations of the particles of the medium are parallel to the direction of wave travel.

• Sound waves consist of compressions and rarefactions.
• Compressions are regions of high pressure.
• Rarefactions are regions of low pressure.
• Energy is transferred without transferring matter.

Reflection of Sound Waves

Reflection of sound occurs when sound waves bounce off a surface.

• Occurs at hard, flat surfaces such as walls or cliffs.
• Produces echoes.
• The angle of incidence equals the angle of reflection.

Application:

• Echo sounding
• Sonar
• Ultrasound imaging

Refraction of Sound Waves

Refraction of sound occurs when sound waves change speed as they travel through regions of air with different properties.

• Sound speed depends on temperature and density of air.
• Sound bends when speed changes.
• This often occurs in the atmosphere.

Examples:

• Sound travelling further at night.
• Sound bending due to temperature layers in air.

Wave Relationship Used

Sound waves obey the wave equation:

\( \mathrm{v = f\lambda} \)

• \( \mathrm{v} \) = speed of sound (m/s)
• \( \mathrm{f} \) = frequency (Hz)
• \( \mathrm{\lambda} \) = wavelength (m)

During refraction, frequency remains constant, but speed and wavelength change.

Key Idea

• Sound waves are longitudinal.
• They consist of compressions and rarefactions.
• Sound can be reflected and refracted.

Important Points to Remember

• Sound cannot travel in a vacuum.
• Reflection produces echoes.
• Refraction occurs due to speed changes.