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NEET Sample Paper NEET Sample Test Paper-68

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

    A) 180 ergs            

    B) 360 ergs

    C) 720 ergs            

    D) 960 ergs

    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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