Physics - Wave Optics Question with Solution | TestHub

The resultant intensity of the interfering waves is given by, ${\mathrm{E}}^2{\mathrm{E}}_1^2+{\mathrm{E}}_2^2+2{\mathrm{E}}_1{\mathrm{E}}_2\cos (\delta )$ where, $\delta$ is the phase difference between the waves. For a dark fringe, ${\mathrm{E}}_1={\mathrm{E}}_2$ and $\cos (\delta )=-1$. Therefore, the phase $\delta =(2n+1)\pi$ is an odd multiple of pi.