For a thin film interference, a fringe for transmission is formed. When 2μx=nλ ⇒dtdx=(dtdn)2μλ=(121)2×1.4560×10−9=35×10−8 m/s V= Volume of film =πR2xdtdV=πR2dtdx=π(1.8×10−2)235×10−8 m3/s=54π×10−13 m3/s
JEE Main 2025 — Physics Mechanics
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×10−13 m3/s.
Held on 28 Jan 2025 · Verified 6 Jul 2026.
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Two wires as shown in the figure below, made of steel and have breaking stress of $12 \times 10^8$ N/m$^2$. Area of cross-section of upper wire is $0.008$ cm$^2$ and of lower wire is $0.004$ cm$^2$. The maximum mass that can be added to pan without breaking any wire is _____ kg. (take $g = 10$ m/s$^2$) 
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When a part of a straight capillary tube is placed vertically in a liquid, the liquid raises upto certain height $h$. If the inner radius of the capillary tube, density of the liquid and surface tension of the liquid decrease by $1 \%$ each, then the height of the liquid in the tube will change by $\%$.
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