Waves: Question 7

Worked solution

Step 1: Recall the defining feature of each wave type

The key distinction between a transverse wave and a longitudinal wave is the direction in which particles of the medium vibrate, relative to the direction in which the wave transfers energy.

• In a transverse wave, particles vibrate perpendicular to the direction of energy transfer (e.g. a wave on a stretched string, or any electromagnetic wave).
• In a longitudinal wave, particles vibrate parallel to (along the same line as) the direction of energy transfer (e.g. sound in air).

Step 2: Match this to the options

Option B states exactly this: transverse $\Rightarrow$ perpendicular vibration, longitudinal $\Rightarrow$ parallel vibration.

Why the other options are wrong

• A: this is the reverse of the correct definitions, it swaps “perpendicular” and “parallel”.
• C: both wave types transfer energy without transferring matter; the claim that only transverse waves transfer energy is incorrect, and longitudinal waves do not vibrate parallel by definition being confused with transverse behaviour here is also wrong.
• D: this swaps the descriptive terms, crests and troughs describe a transverse wave’s shape, while compressions and rarefactions describe a longitudinal wave’s regions of particle bunching and spreading.

Final answer

• The correct description is $\boxed{\text{option B}}$: transverse $=$ perpendicular vibration, longitudinal $=$ parallel vibration.