Ratio of intensities between a point A and that of central fringe is 0.853. Then path difference between two waves at point A will be
Answer & explanation
Correct answer: option 3
$R^2=a^2+b^2+2 a b \cos \phi$
$\frac{I_R}{I_{\max }}=0.853$
∴ $I_R=0.853 ~I_{\max }=0.853 \times 4 I$
$I_R=I+I_0+2 I \cos \phi=2 I(1+\cos \phi)=0.853 \times 4 I$
$\Rightarrow \phi=\frac{\pi}{4}=\frac{\lambda}{8}$