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9th Class Science Sound Question Bank Sound

  • question_answer
    A sound has an intensity of \[3\times {{10}^{-8}}W/{{m}^{2}}\].What is the sound level in dB (decibels)?       (Given,\[\log \,\,3=0.477\])                  

    A)  4.477 dB        

    B)         0.4477 dB    

    C)  44.77 dB          

    D)         44.7 dB      

    Correct Answer: C

    Solution :

         \[dB=10\log \left[ \frac{3\times {{10}^{-8}}}{1\times {{10}^{-12}}} \right]\]                 \[=101og(3\times {{10}^{4}})\]                 \[=10[4+\log 3]\]                 \[=10[4+0.477]\]                 \[=10\times 4.477\]                 \[=44.77\,\,dB\]


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