Two coherent point sources \( S_1 \) and \( S_2 \) vibrating in phase emit light of wavelength \( \lambda \). The separation between them is \( 2\lambda \). The light is collected on a screen placed at a distance \( D \gg \lambda \) from the slit \( S_1 \) as shown. The minimum distance, so that intensity at \( P \) is equal to intensity at \( O \), is:
