Sound propagates as density variations.
Explanation
Sound is a mechanical wave that requires a material medium for propagation. It travels through the vibration of medium particles, transferring energy from one point to another. The nature of this propagation depends on the physical properties of the medium, such as elasticity and inertia.
Option Analysis
- Sound propagates as a transverse wave in fluids. is Incorrect. In fluids (liquids and gases), sound propagates exclusively as longitudinal waves. Transverse waves require the medium to possess shear strength (rigidity) to sustain perpendicular vibrations, a property found in solids but not in fluids.
- Sound propagates as density variations. is Correct. Sound propagates through a medium as a series of compressions (regions of high pressure and high density) and rarefactions (regions of low pressure and low density). Therefore, sound waves can be described as the propagation of density or pressure variations.
- Sound propagates without any energy transfer. is Incorrect. A fundamental property of all waves, including sound, is the transfer of energy and momentum. While matter is not transported, energy is transmitted from the source to the receiver through particle interaction.
- Sound propagates by the physical movement of medium from source to receiver. is Incorrect. During sound propagation, the particles of the medium do not physically travel from the source to the receiver. Instead, they oscillate back and forth about their mean equilibrium positions, passing the disturbance to adjacent particles.
Key Takeaway
Sound waves in fluids are longitudinal mechanical waves characterized by the transfer of energy through density and pressure variations (compressions and rarefactions) without the net transport of the medium itself.