NEET Sample Paper NEET Sample Test Paper-14

  • question_answer The work done against surface tension in blowing a soap bubble from a radius 10 to 20 cm, if the surface tension of solution is \[25\times {{10}^{-3}}N/m,\] is

    A) \[3\pi \times {{10}^{-3}}J\]             

    B) \[6\pi \times {{10}^{-3}}J\]

    C) \[2\pi \times {{10}^{-3}}J\]             

    D) \[4\pi \times {{10}^{-3}}J\]   

    Correct Answer: B

    Solution :

    Initial total surface area\[{{A}_{1}}=2\times 4\pi {{(v)}^{2}}{{m}^{2}}.\] Final total surface area \[{{A}_{2}}=2\times 4\pi {{(0.2)}^{2}}{{m}^{2}}.\] Work done against surface tension,\[W=S\,({{A}_{2}}-{{A}_{1}})\] \[\therefore \]\[W=25\times {{10}^{-3}}\times 8\pi (0.04-0.01)=6\pi \times {{10}^{-3}}J\] Hence, the correction option is [b].

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