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NEET Sample Paper NEET Sample Test Paper-70

  • question_answer
    The radius of a soap bubble is increased from\[\frac{1}{\sqrt{\pi }}\,cm\,\,to\,\,\frac{2}{\sqrt{\pi }}\]. If the surface tension of water is 30 dynes per cm, men the work done will be                                 

    A) 180 erg           

    B) 360 erg        

    C) 720 erg           

    D) 960 erg          

    Correct Answer: C

    Solution :

    \[W=8\pi T(r_{2}^{2}-r_{1}^{2})=8\pi T\,\left[ {{\left( \frac{2}{\sqrt{\pi }} \right)}^{2}}-{{\left( \frac{1}{\sqrt{\pi }} \right)}^{2}} \right]\] \[\therefore \,\,\,\,\,\,W=8\times \pi \times 30\times \frac{3}{\pi }=720\,erg\]


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