A thin transparent film with refractive index 1.4 , is held on circular ring of radius 1.8 cm . The fluid in the film evaporates such that transmission through the film at wavelength 560 nm goes to a minimum every 12 seconds. Assuming that

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A thin transparent film with refractive index 1.4 , is held on circular ring of radius 1.8 cm . The fluid in the film evaporates such that transmission through the film at wavelength 560 nm goes to a minimum every 12 seconds. Assuming that the film is flat on its two sides, the rate of evaporation is ____ 10⁻¹³ ~m ^3 / s .

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For a thin film interference, a fringe for transmission is formed. When 2 x=n aligned & d x d t = ( d n d t ) 2 & = ( 1 12 ) 560 10⁻⁹ 2 1.4 = 5 3 10⁻⁸ ~m / s aligned aligned & V= Volume of film = R^2 x & d V d t = R^2 d x d t & = (1.8 10⁻² )^2 5 3 10⁻⁸ ~m ^3 / s & =54 10⁻¹³ ~m ^3 / s aligned

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