[pls explain the filter concept.......when white light is passed through yellow light...........then which colours come out through it?????

The 3 primary colours of light are red, blue & green.

The secondary colors of light are those colors which are formed when two primary colors are mixed in equal amounts.
Mixing blue and green light results in cyan light.
Mixing red and blue light results in magenta light.
And mixing red and green light results in yellow light.

Filters can be thought of as absorbing one or more of the primary colors of light which are incident upon it, allowing remaining colors to be transmitted. For instance, a green filter will absorb all wavelengths except for green light. In this sense, filters subtract colors from the mix of incident light, allowing only selected colors to pass through.

When white light is first passed through a yellow filter, all colours are absorbed except the yellow light (i.e.red+green pass through & blue is absorbed).