In a double-slit experiment, green light (5303 Å) falls on a double slit having a separation of 19.44 μm and a width of 4.05 μm. The number of bright fringes between the first and the second diffraction minima is?

For diffraction:
Location of 1st minima y1 = Dλ/a = 0.2469Dλ
Location of 2nd minima y2 = 2Dλ/a = 0.4938Dλ
Now for interference:
Path difference at P: dy/D = 4.8λ
path difference at Q: dy/D = 9.6λ
So orders of maxima in between P and Q is 5, 6, 7, 8, 9
So 5 bright fringes are present between P and Q.