In Young's double slit experiment, if the widths of the slit are in the ratio 4 : 9, ratio of intensity of maxima to intensity of minima will be

25 : 1

As ratio of slit widths = Ratio of intensities

$∴\frac{I_1}{I_2}=\frac{9}{4}$ or $\frac{a1^2}{a2^2}=\frac{9}{4}$ or $\frac{a1}{a2}=\frac{3}{2}$

$a_{max} = a_1 + a_2 = 3 + 2 =5; a_{min.} = 3 - 2 = 1$

$\frac{I_{max}}{I_{min.}}=\frac{(a1+a2)^2}{(a1-a2)^2}=\frac{(3+2)^2}{(3-2)^2}=\frac{25}{1}$