posted by alliyu .
when a transparent vessel is is filled with water and a jet flows out of the vessel with a light source placed so that a horizontal beam enters the liquid jet. Under what conditions does the jet operate like a light candle?
By "light candle" I assume you mean "light pipe". Maybe I am using a more old-fashioned term for it.
The incidence angle of the light hitting the walls of the jet from the inside must be greater than the "critical" angle for total reflection, sin^-1 (1/1.33), which is 49 degrees.