A plastic sheet (refractive index =1.6) covers one slit of a double slit arrangement meant for the Young's experiment. When the double slit is illuminated by monochromatic light (wavelength in air\[=6600\,\overset{o}{\mathop{A}}\,\]), the centre of the screen appears dark rather than bright. The minimum thickness of the plastic sheet to be used for this to happen is:

• A. \[3300\overset{o}{\mathop{A}}\,\]
• B. \[6600\overset{o}{\mathop{A}}\,\]
• C. \[2062\overset{o}{\mathop{A}}\,\]
• D. \[5500\overset{o}{\mathop{A}}\,\]