If two planes intersect do they intersect in exactly one plane?

The intersection of two planes is a line. (or a massive explosion...lol)

yes but they shouldn't run into eachother if they have there lights on

No, 2 planes may only intersect at a line, a plane, or not at all. THREE planes may intersect at a point though...

There must be something missing from the question. As it stands, what's the big deal ? The wall of a room intersects four other planes . . . two walls, the floor, and the ceiling.

Yes, the intersection of 2 planes is a line.