A) 25 N
B) 20 N
C) 14 N
D) 28 N
Correct Answer: D
Solution :
Surface tension (T) is defined as the force required to separate the surface area (A A) of liquid film by unity at constant temperature. \[T=\frac{W}{\Delta \,A}\] ? (i) Since film of water consists of two films hence twice of surface area is taken. Also, W = force (.F) x displacement ...(ii) From Eqs. (i) and (ii) and taking twice of surface area, we get \[F=\frac{2T\Delta A}{d}\] Given, \[\Delta A={{10}^{-2}}{{m}^{2}}\], \[T=70\times {{10}^{-3}}N/m\], \[d=0.5\,mm=0.05\times {{10}^{-3}}m\] \[\therefore \] \[F=\frac{2\times 70\times {{10}^{-3}}\times {{10}^{-2}}}{0.05\times {{10}^{-3}}}=28\,N\]You need to login to perform this action.
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