Longitudinal waves have particle vibrations parallel to propagation direction

Steps:

• Recall that longitudinal waves feature oscillations parallel to the wave's travel direction, like compressions and rarefactions in sound.
• Identify wave types: electromagnetic waves (gamma, light, X-rays) are transverse with perpendicular oscillations; sound waves (ultrasound) are longitudinal.
• Match choices: A, B, D are electromagnetic; C is acoustic sound.
• Select C as the only longitudinal example.

Why C is correct:

• Ultrasound waves are mechanical sound waves propagating through media via particle compression and expansion, defining longitudinal motion per wave classification.

Why the others are wrong:

• A: Gamma rays are electromagnetic waves with transverse electric and magnetic field oscillations.
• B: Light waves are electromagnetic, vibrating perpendicular to propagation.
• D: X-rays are electromagnetic waves, transverse like visible light.

Final answer: C