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

Question

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 ____ π × 1 0 − 13 m 3 / s .

TestHub · Accepted Answer

For a thin film interference, a fringe for transmission is formed. When 2 μx = nλ ⇒ ​ d t d x ​ = ( d t d n ​ ) 2 μ λ ​ = ( 12 1 ​ ) 2 × 1.4 560 × 1 0 − 9 ​ = 3 5 ​ × 1 0 − 8 m / s ​ ​ V = Volume of film = π R 2 x d t d V ​ = π R 2 d t d x ​ = π ( 1.8 × 1 0 − 2 ) 2 3 5 ​ × 1 0 − 8 m 3 / s = 54 π × 1 0 − 13 m 3 / s ​

Physics - Fluid Question with Solution | TestHub

Doubts & Discussion