1. To create a uniform and consistent interference pattern:
* Point source: If a point source were used, the light would be diffracted by the lens and the resulting interference pattern would be very complex and difficult to analyze. This is because the light rays from a point source would arrive at the lens from different angles, leading to variations in path length and thus, interference.
* Extended source: Using an extended source ensures that light rays from different points on the source reach the lens at a variety of angles. This creates a large number of overlapping interference patterns. However, due to the nature of the experiment, only the central portion of this pattern will be observable as a clear and consistent set of rings. This central portion is where the path differences between the reflected rays are most uniform.
2. To enhance the visibility of the interference pattern:
* Point source: The intensity of the interference pattern would be very low with a point source. This is because only a small amount of light would be diffracted by the lens.
* Extended source: The extended source provides a much greater intensity of light, making the interference pattern more visible. This is because more light rays contribute to the formation of the interference pattern.
In summary:
An extended source in Newton's rings experiment helps to create a uniform and consistent interference pattern that is more visible than what could be achieved with a point source. This is essential for accurate measurements of the wavelength of light and the radius of curvature of the lens.
