The level of water in a clear, colorless glass is easily observed with the naked eye. The level of liquid helium in a clear glass vessel is extremely difficult to see with the naked eye. Explain. (hint: the index of refraction of liquid helium is close to that of air.)
The difference in visibility between the water and liquid helium in a clear glass vessel can be explained by the concept of refraction and the index of refraction.
Refraction occurs when light passes through a medium with a different refractive index, causing the light to change direction. The refractive index is a measure of how fast light travels in a particular medium compared to its speed in a vacuum. Different substances have different refractive indices, and this property affects how they interact with light.
Water has a higher refractive index compared to air, which means that light travels slower through water than it does through air. As a result, when light passes from air into water, it bends or refracts. This bending of light causes objects submerged in water to appear shifted or distorted compared to how they would appear in the air. This bending effect also makes the water level in a glass easily visible to the naked eye.
Liquid helium, on the other hand, has a refractive index that is very close to that of air. This means that light travels at nearly the same speed through liquid helium as it does through air. As a result, when light passes from air into liquid helium, there is little to no bending or refraction of the light rays. This lack of refraction makes it extremely difficult to distinguish the liquid helium from the surrounding air, even when observed through a clear glass vessel.
So, even though the liquid helium is present in the glass, its level is difficult to discern because the refractive index of liquid helium is similar to that of the air, minimizing the bending or refraction of light that would make it visible to the naked eye.