When a beam of light shines through a green filter then a red filter. What will happen?
No light will pass through both filters if they are narrow band filters. The green filter lets only green light through (wavelength about 500-550 nm) and the red filter lets only red light through (about 620-670 nm). After passing through the green filter, only 500-550 nm light is left, and the red filter blocks everything but 620-670 nm, but there isn’t any of that.
