In Fresnel’s biprism experiment the width of  10  fringes is 2 cm  which are formed at a distance of two 2  meter from the slit. If the wavelength of light is  5100 A0  then the distance between two coherent sources will be

Wavelength λ=5100 A0=5100×10−10  m Fringe width β=210 cm=210×10−2 m Distance between slit and screen D=2 m Distance between two coherent sources d=? ⇒d=Dλβ   ( ∵ β=λDd )                                                     =2×51×10−82×10−3=5.1×10−4m ∴  d=5.1×10−4 m