In Young’s double slit experiment, the fringes are displaced by a distance when a glass plate of refractive index 1.5 is introduced in the path of one of the beams. When this plate is replaced by another plate of the same thickness, the shift of fringes is . The refractive index of the second plate is
The fringe shift with first plate is given by
For second plate the shift is given by
Divide (2) by (1)