Sound waves cannot travel through which of the following?

Appeared in: RML Lucknow - 2021

Explanation

Sound waves are classified as mechanical waves, meaning they require a medium composed of particles to propagate.
A vacuum is defined as a space devoid of matter, and therefore, it lacks the particles necessary for sound wave transmission.
The vibrations that constitute a sound wave cannot be created or passed along in the emptiness of a vacuum.

Option A: Water is a liquid medium. Sound can and does travel through water. In fact, it travels significantly faster in water (approx. 1480 m/s) than in air because the molecules are closer together.
Option B: Steel is a solid medium. Sound travels very efficiently and quickly through solids like steel (approx. 5960 m/s) because the particles are tightly packed, allowing for rapid transfer of vibrations.
Option C: Air is a gaseous medium and is the most common medium through which we experience sound. Sound travels through air by compressing and rarefying air molecules.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Propagation of Sound Waves as background academic context rather than a clinical decision trigger.
This principle is fundamental to understanding medical ultrasonography. Ultrasound uses high-frequency sound waves to create images of internal body structures.
A coupling gel is applied to the skin during an ultrasound exam to eliminate any air pockets between the transducer and the skin. Since sound cannot travel through the air (or travels very poorly), the gel ensures an unbroken medium for the sound waves to pass into the body, allowing for a clear image.
What if? If a clinician performed an ultrasound without using coupling gel, the air gap between the transducer and the patient's skin would reflect almost all the sound waves, preventing them from entering the body. The result would be a very poor or completely blank image, making diagnosis impossible.

How to Approach the Question

First, identify the core scientific concept in the question, which is the nature of 'sound waves'.
Recall the fundamental property of sound: it is a mechanical wave. This is the key piece of knowledge.
Define what a 'mechanical wave' is: a wave that needs a medium (solid, liquid, or gas) to transfer energy.
Evaluate each option against this requirement: Water (liquid), Steel (solid), and Air (gas) are all media.
Identify the option that is NOT a medium. A 'vacuum' is the absence of a medium.
Conclude that since sound needs a medium and a vacuum has none, sound cannot travel through a vacuum.

Concept Tested & Keywords

Concept Tested: Propagation of Sound Waves
Stem keywords: Sound waves, travel through
Lead-in keywords: cannot
Negative lead-in flag: The question asks what sound CANNOT travel through, which is a negative framing.

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E6 Psychology Morgan King 9e Part 1 p. 114-116

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