The glass plate in a Newton's ring experiment is not typically inclined at 45 degrees. Instead, it's nearly flat and parallel to the plano-convex lens. Here's why:

* Formation of Interference: The Newton's rings are formed due to interference between light reflected from the top surface of the plano-convex lens and the bottom surface of the plane glass plate. For interference to occur, the reflected beams need to be nearly parallel.

* Angle and Interference: If the glass plate were inclined at 45 degrees, the reflected beams would be at a significant angle to each other, leading to poor interference.

* Clear Ring Pattern: The slight tilt of the glass plate is intentional to create a wedge-shaped air film between the lens and the plate. This wedge creates varying thicknesses of air, leading to the formation of concentric rings of alternating bright and dark bands.

In summary: The glass plate in a Newton's ring experiment is nearly flat and parallel to the lens to ensure good interference. A slight tilt is introduced to create a wedge-shaped air film, which is crucial for the formation of the distinctive rings.