In Young's double slit experiment, 'I' is the minimum intensity and ' I_1 ' is the intensity at a point where the path difference is \frac{\lambda}{4} where ' \lambda ' is the wavelength of light used. The ratio I_1 \mathrm{I}_1 is (Intensities of the two interfering waves are same) \left(\cos 0^{\circ}=1, \cos 90^{\circ}=0\right)