Which of the following waves is both transverse and mechanical?

Analysis

To solve this, we need to understand two key classifications of waves:

1. Mechanical Waves: These require a material medium (solid, liquid, or gas) to travel. They cannot travel through a vacuum.
2. Transverse Waves: These are waves where the particles of the medium vibrate perpendicularly (at 90 degrees) to the direction of wave propagation.

Concept Explanation

• Mechanical vs. Electromagnetic: Sound waves and water waves are mechanical. Radio waves and X-rays are electromagnetic waves (they do not require a medium and can travel through a vacuum).
• Transverse vs. Longitudinal: • Transverse: Particles move up and down (perpendicular) as the wave moves forward. Examples include waves on a string and water waves. • Longitudinal: Particles move back and forth (parallel) in the same direction as the wave. Sound waves are the classic example of longitudinal waves.

Step-by-Step Solution

1. Evaluate Radio waves and X-rays: These are electromagnetic waves. Since they do not require a medium, they are not mechanical. We eliminate options B and D.
2. Evaluate Sound waves: Sound waves are mechanical, but they are longitudinal because the air particles vibrate parallel to the direction of the sound. We eliminate option C.
3. Evaluate Water waves: Water waves require a medium (water) to travel, making them mechanical. As the wave moves across the surface, the water particles move up and down (perpendicular to the direction of the wave), making them transverse.

Conclusion

Water waves satisfy both conditions: they are mechanical (need water) and transverse (particles move perpendicularly).

Exam Tip: Remember the acronym "EM-L" for Electromagnetic waves (Radio, X-rays, Light, etc.)—they are all transverse but not mechanical. Sound is the only common mechanical wave that is longitudinal. Everything else mechanical (like ripples on a pond or waves on a string) is transverse.