What effect does increasing the wedge angle have on the spacing of interference fringes? If the wedge angle is too large, fringes are not observed. Why?

Coherent light is a type of light whose waves are in phase, or whose phase difference remains constant over time. It is a key component in many optical experiments because it allows for predictable interference patterns. Coherent light is typically produced by lasers or other specialized light sources. The coherence ensures that the phase difference due to the path difference remains constant, which is crucial for the formation and observation of stable interference fringes.

The concept of path difference is fundamental to understanding how interference fringes are formed. It is defined as the difference in the distance traveled by two waves from a common source to a specific point. In a wedge-shaped medium, the thickness varies linearly, and so does the path length that the light waves must travel. This path difference gives rise to a phase difference between the waves when they emerge from the medium.

As the wedge angle changes, the path difference and consequently the phase difference between the light waves also change. This can either increase or reduce the visibility of the interference fringes, depending on the wavelength of the light and the resolving power of the observing equipment or the human eye. For small wedge angles, interference fringes are distinctly visible, but as the wedge angle becomes larger, and moreover, the threshold of resolution is surpassed, the fringes may no longer be distinguishable.

Understanding the relationship between path difference, coherence, and the observation of interference patterns is critical for students studying wave optics, as it helps explain various phenomena not just in the classroom but in real-world applications as well.