The velocity of sound waves and electromagnetic waves behaves differently with respect to depth due to the properties of the media through which they propagate.
For sound waves, their velocity is primarily influenced by the properties of the medium they travel through, such as density and elasticity. As depth increases in a medium like water or air, the pressure also increases. In general, an increase in pressure results in an increase in density and compressibility of the medium. Since sound waves rely on the compressibility of the medium to propagate, the increased density and compressibility at greater depths cause a decrease in the velocity of sound waves.
On the other hand, electromagnetic waves, such as light or radio waves, do not require a medium to propagate and can travel through vacuum or different materials. In the context of depth, the behavior of electromagnetic waves depends on the specific characteristics of the medium they encounter.
In many cases, as depth increases in a medium like water or glass, the refractive index of the medium typically increases. The refractive index measures how much the speed of light is reduced when it enters a particular medium compared to its speed in a vacuum. Since the refractive index increases with depth, the velocity of electromagnetic waves also increases because they tend to slow down less as they travel deeper into the medium.
It's important to note that these explanations are simplified and may not apply universally to all situations. The behavior of waves can be influenced by various factors, including temperature, pressure, and the specific properties of the medium involved.