Which one of the following is not a transverse wave under ordinary conditions?

Introduction / Context:
Waves can be broadly classified as transverse or longitudinal, depending on the direction in which particles of the medium vibrate relative to the direction of wave propagation. This question tests whether you can correctly identify which wave, from a list of common examples, is not a transverse wave under normal circumstances. Understanding this classification is fundamental in wave physics and helps in interpreting many natural phenomena.

Given Data / Assumptions:

• We are comparing light waves, radio waves and sound waves.
• We assume sound waves in air under ordinary conditions.
• We are asked to find which is not a transverse wave.
• Transverse waves have oscillations perpendicular to the direction of propagation, while longitudinal waves have oscillations parallel to that direction.

Concept / Approach:
Electromagnetic waves, which include light and radio waves, are inherently transverse. In these waves, electric and magnetic field vectors oscillate perpendicular to the direction in which the wave travels. On the other hand, ordinary sound waves in air are mechanical longitudinal waves: air particles oscillate back and forth along the direction of propagation, creating compressions and rarefactions. To answer the question, we must therefore select sound waves as the example that is not transverse.

Step-by-Step Solution:
Step 1: Recall that light waves are electromagnetic waves. Their electric and magnetic fields oscillate perpendicular to the direction of propagation, so they are transverse. Step 2: Recall that radio waves are also electromagnetic and share the same transverse nature as visible light. Step 3: Consider sound waves in air. These require a material medium and consist of compressions and rarefactions along the line of travel. Step 4: In sound waves in air, particle displacement is parallel to the direction of wave propagation, which is the definition of a longitudinal wave. Step 5: Therefore, sound waves, not light or radio waves, are not transverse under ordinary conditions.

Verification / Alternative check:
Physics texts clearly state that electromagnetic radiation (light, radio, microwaves, X-rays and so on) is transverse, whereas standard sound waves in gases and liquids are longitudinal. In solids, sound can have both longitudinal and transverse components, but the typical school-level example of sound in air is purely longitudinal. The option “All of the above” would only be correct if each listed wave were not transverse, which contradicts well established theory. Thus, the only correct choice is sound waves.

Why Other Options Are Wrong:
Light waves: These are transverse electromagnetic waves and do not qualify as “not transverse.”
Radio waves: Also electromagnetic and transverse, used for communication over long distances.
All of the above: Incorrect because only sound waves in air are longitudinal; light and radio waves remain transverse.

Common Pitfalls:
Some students assume that all waves are the same and forget the distinction between electromagnetic and mechanical waves. Others may have heard about transverse vibrations in guitar strings and think sound in air behaves similarly. Remember that in electromagnetic waves, no material medium is needed and the fields oscillate perpendicular to the direction of travel, while in ordinary sound in air, compression and rarefaction occur along the direction of propagation, making them longitudinal.

Final Answer:
The wave that is not transverse under ordinary conditions is Sound waves.