Step 1: Understanding the Concept:
Newton's rings are an interference pattern caused by the reflection of light between two surfaces: a spherical surface and an adjacent flat surface.
Step 2: Detailed Explanation:
In the standard Newton's rings experiment, a plano-convex lens with a large radius of curvature is placed with its convex spherical surface on a flat glass plate.
This arrangement encloses a thin film of air between the lens and the glass plate.
The thickness of this air film is zero at the point of contact (the center) and gradually increases radially outwards.
Due to this continuously increasing thickness from the center towards the periphery, the air film effectively behaves as a wedge-shaped film in any given cross-section.
Step 3: Final Answer:
The shape of the air film formed is wedge-shaped.