A test tube partially filled with water and tilted slightly is partially immersed in a beaker of water Why does the partially airy submerged part of the test tube appear shiny?
Answer: A test tube partially filled with water and partially immersed in a beaker with a slight tilt makes the partially airy submerged part of the test tube shiny. Such is the case for the internal total reflection of light. The aqueous portion of the test tube appears transparent. Because the incident light is not fully reflected in this part, but because the medium inside and outside the test tube is water, the light is refracted. As a result, the watery part does not shine.
But in the upper hollow, which is airy, light rays pass from the denser medium water to the lighter medium air. In this case, the rays whose angle of incidence is greater than the angle of refraction of water and air, the total internal reflection of those rays takes place. As a result, the empty part of the test tube becomes shiny.