Question

When monochromatic light is replaced by white light in Fresnel's biprism arrangement, the central fringe is

• A. colored
• B. white
• C. dark
• D. None of these

Answer 1

Answer: (B)

white

When white light refracts from the biprism, all colours would form coherent sources at different positions according to their refractive indices. However the position of their central fringe would be same, and hence they would all combine at that position to again give a white fringe.