Question

A light source is made to pass through a narrow slit in a window how do you think the light rays will travel

Answer 1

They will diffract and create an interference pattern. (See two-slit method)

Answer 2

Light will travel in straight lines.

Step-by-step explanation:

This is the effect your are going to see. If you have two narrow slits then you are going to see another phenomenon, diffraction and interference, because the two light waves with encounter one another after passing the two narrow slits.