The two coherent sources produce interference with intensity ratio ' $b$ '. In the interference pattern, the ratio $\frac{I_{\text {max }}+I_{\text {min }}}{I_{\text {max }}-I_{\text {min }}}$ will be

According to Huygen's wave theory of light, which one of the following statements is not correct?

Interference fringes are produced on the screen by using two light sources of intensities I and 9I. The phase difference between the beams is $\pi / 2$ at point P and $\pi$ at point Q on the screen. The difference between the resultant intensities at points P and Q is $\left(\cos 90^{\circ}=0, \cos \pi=-1\right)$

In Young's double slit experiment, in an interference pattern, a minimum is observed exactly in front of one slit. The distance between the two coherent sources is d and $\mathrm{D}_{\text { }}$ is the distance between source and screen. The possible wavelengths used are proportional to