Question

Due to effect of interference, floating oil layer in water in visible coloured, due to observation of this event the thickness of oil layer should be :

• A. $10nm$
• B. $1\mu m$
• C. $1mm$
• D. $10mm$

Answer 1

The correct option is B $1\mu m$

$Forconstructiveinterferenceinthereflectedsystem,\Rightarrow 2\mu tcosr=(2n+1)\frac{\lambda }{2}\Rightarrow 2\times 1.4\times tcos\theta =(2n+1)\frac{{5600\times 10}^{-10}}{2}\Rightarrow t=(2n+1)\frac{{5600\times 10}^{-10}}{5.6}\Rightarrow t=(2n+1)\times 1000\times 10^{-10}\Rightarrow t=(2n+1)\times 10^{-10}Forn>5,twillbetheorderof10m.Therefore,thecorrectoptionis\left(1\right).$