In a medium, the nature of sound waves is

Question

Accepted Answer

The correct answer is Option 4: only longitudinal.

Here's a detailed explanation:

**Justification for Option 4 (only longitudinal) being correct:**

Sound waves are mechanical waves, meaning they require a medium (like air, water, or solids) to travel. Their propagation involves the oscillation of particles within that medium.

1.  **Mechanism of Sound Propagation:** Sound travels through a series of compressions (regions of higher pressure and density) and rarefactions (regions of lower pressure and density).
2.  **Particle Oscillation:** In a sound wave, the particles of the medium oscillate back and forth *parallel* to the direction in which the wave is traveling. For example, if sound is moving from left to right, the air molecules will vibrate left and right around their equilibrium positions.
3.  **Definition of Longitudinal Wave:** A wave in which the particles of the medium oscillate parallel to the direction of wave propagation is defined as a longitudinal wave.
4.  **Universality:** This characteristic (longitudinal motion) is fundamental to sound propagation in all types of media – gases, liquids, and solids. While solids can also support transverse (shear) waves, the primary and universal nature of sound, particularly the pressure wave component, is longitudinal. Gases and liquids, which are common media for sound, *only* support longitudinal sound waves because they cannot sustain shear stress. Therefore, "only longitudinal" accurately describes the fundamental and universally present nature of sound waves.

**Explanation for why other options are incorrect:**

*   **Option 1: only transverse**
    *   This option is incorrect because transverse waves are characterized by particle oscillation *perpendicular* to the direction of wave propagation. While light waves are transverse, sound waves are not primarily or exclusively transverse. In gases and liquids, sound waves cannot be transverse at all. Even in solids, while transverse sound waves (shear waves) can exist, they are not the *only* type of sound wave, and the fundamental pressure wave is longitudinal.

*   **Option 2: both longitudinal and transverse**
    *   This option is incorrect because it is not universally true for all media. While solids can support both longitudinal (compressional) and transverse (shear) sound waves, liquids and gases *only* support longitudinal sound waves. Since the question asks for "the nature of sound waves" in "a medium" (implying a general characteristic), stating "both" is misleading as it doesn't apply to all common media for sound propagation. The most fundamental and universally applicable nature of sound is longitudinal.

*   **Option 3: neither longitudinal nor transverse**
    *   This option is incorrect because sound waves are mechanical waves and, by definition, must involve particle displacement relative to the direction of propagation. All mechanical waves are classified as either longitudinal, transverse, or a combination/superposition of these modes. Therefore, sound waves must fall into one of these categories; they cannot be neither.