Sound waves are mechanical longitudinal waves and require a material medium for their propagation. Through which one of the following arrangements can sound waves not travel at all?

Introduction / Context:

Unlike electromagnetic waves, sound waves need a material medium such as gas, liquid or solid to propagate. They travel by setting particles of the medium into vibration. A classic conceptual test in physics exams is to ask which situation would prevent sound from propagating because of the absence of a suitable medium. This question presents different materials placed in different environments and asks where sound waves cannot travel at all.

Given Data / Assumptions:

• Sound waves are mechanical and require matter to propagate.
• Solids, liquids and gases can act as media for sound.
• Vacuum does not provide particles for vibration, so sound cannot pass through vacuum.
• The options involve different combinations of materials and surroundings.

Concept / Approach:

Sound propagation depends on the presence of material particles that can oscillate and transmit the disturbance. Metals like copper and silver, glass, water and wood are all capable of transmitting sound because they contain atoms and molecules. However, in a perfect vacuum, there are no particles to support the mechanical vibrations required for sound. Even if you place a hollow object in a vacuum, the space inside and outside is void of air or any material medium, so sound cannot travel through that region.

Step-by-Step Solution:

Verification / Alternative check:

The classic school experiment placing a ringing bell inside a bell jar and gradually evacuating the air demonstrates that as air is removed, the sound becomes fainter and ultimately disappears when near vacuum is achieved. This shows clearly that sound cannot travel through vacuum. In contrast, solid bars and liquids are known to transmit sound effectively, often better than gases.

Why Other Options Are Wrong:

Option A: Copper wire in air provides two media, solid and gas, both capable of carrying sound, so sound can propagate.

Option B: Silver slab in air also offers solid and gaseous media and does not prevent sound transmission.

Option C: Glass prism in water combines a solid and a liquid, both of which can transmit sound waves.

Common Pitfalls:

Some students may incorrectly think that sound cannot travel in solids or that only air transmits sound. In fact, sound travels fastest in solids and more slowly in liquids and gases. The only environment in which sound cannot propagate is vacuum, where there are no particles to oscillate. Always look for the presence or absence of a material medium when answering propagation questions.

Final Answer:

Sound waves cannot travel through a wooden hollow pipe placed in vacuum.