Physics problem that I don't completely understand?
A spotlight is coated so that it won't transmit yellow light from its white-hot filament. What color is the emerging beam of light?
The "white-hot" filament gives off white light. White light is a mixture of light which has some red light, some green light, and some blue light. The coating "filters" the light by stopping the yellow light from getting through it at all. "Black" is the absence of light, so there is no such thing as "black light". Some of the colors which we see are really mixtures of other colors, as is the yellow light stopped by the coating. If you know or were told by the teacher what colors mix to produce the color yellow, you should be able to figure out from the clues I have given here which one of the answers in the list is NOT ruled OUT by these clues.