Question

why can we see the part of the Dust particles when the sunlight passes through a slit is left open between the windows

Answer 1

we can see the dust particles when the sun light passes through slit left open between the window because :- when the light ray hits the dust particle, it gets catered and entes your eyes , but in general,the light just hits the dust particle,and due to high focus in the room your eye will not be able to catch the light scattered by the dust particle