A Fresnel biprism arrangement is shown. Which listed modifications would definitely increase the number of interference fringes obtained on the screen?

Question

G1 Physics · Accepted Answer

For a Fresnel biprism, fringe width decreases when wavelength decreases, and the number of observable fringes also increases when the useful overlap region increases. Moving the source farther away increases the overlap region, and decreasing λ reduces β. Thus modifications 1 and 3 increase the count. Option D.