why doesn't white light disperse into a color spectrum when it passes through a flat window glass?

Answer 1

Because it exits the glass at the same angle as it enters. In a prism, the light goes through different amounts of glass, which causes different levels of bending as it exits. That is the easiest way to describe it without getting too technical.

Answer 2

White light consists of a range of colors. For every wavelength, there is a different angle of refraction when it enters the prism. While passing through the prism, the colors will follow unparallel paths. But when they reach the surface going back to the original medium (probably the air) each color refracts again. The angle is the same angle, but with a minus sign. In a prism the 2 surfaces are not parallel, so the colors head off at an angle to the original path but the colors are again parallel. If instead of a prism, they went through a thick piece of glass, then they each return to the original compass heading - just offset to the side a bit.

Answer 3

Flat glass just lets light pass straight through, so it's the same on one side as the other. A prism deflects light. I do not mean in a different direction alone. BUT each time light is reflected or deflected, it loses strength. When the light rays are diminished in length, they are a different colour. The angle of deflection can alter the colour.

Answer 4

Dispersion is caused by the change of refractive index of the material as a function of frequency. If the light comes in parallel or normal to the glass, there is no net refraction and therefore no dispersion