A transverse wave and a longitudinal wave travelling in the same direction in a medium differ essentially in their

1. Analyze the question We are comparing a transverse wave and a longitudinal wave moving in the same direction through a medium. The question asks what essentially (fundamentally) distinguishes them.

2. Explain the concept

• Transverse wave: the particles of the medium vibrate perpendicular (at right angles) to the direction the wave travels. Examples are water waves, light waves and waves on a string.
• Longitudinal wave: the particles of the medium vibrate parallel (back and forth along) the direction the wave travels. Examples are sound waves and compression waves in a spring. They form compressions and rarefactions.

3. Solution: checking each option

• A. Frequency: Both types of wave can have any frequency, so this does not define the difference.
• B. Amplitude: Both can have any amplitude, so this does not define the difference.
• C. Direction of vibration of the particles of the medium: This is the defining difference. In a transverse wave the vibration is perpendicular to the direction of travel, and in a longitudinal wave it is parallel to it. ✔
• D. Period of vibration: Both can have any period, so this does not define the difference.

4. Answer The correct option is C, the direction of vibration of the particles of the medium.

5. Exam tip Remember "Transverse = Thwart (across), Longitudinal = Long (along)". Whenever a question asks how the two wave types differ, think about the particle vibration direction relative to the wave direction. Frequency, amplitude and period are properties that both wave types share.