NEET Sample Paper NEET Sample Test Paper-47

  • question_answer
    A wire of resistance \[{{\operatorname{R}}_{o}}\]is elongated 'n' fold to make a new uniform wire. The resistance of new wire is:

    A) \[{{\operatorname{nR}}_{o}}\]                          

    B) \[{{\operatorname{n}}^{2}}{{R}_{o}}\]    

    C) \[2{{\operatorname{nR}}_{o}}\]                        

    D) \[2{{n}^{2}}{{R}_{o}}\]

    Correct Answer: B

    Solution :

    \[{{\ell }_{1}}={{\ell }_{\operatorname{o}}}\,\,\,\,\,\,\,\,\,\,\,{{\ell }_{2}}=\operatorname{n}{{\ell }_{o}}\] If wire is elongated but its volume remains constant \[\operatorname{V}{{~}_{initial}}={{V}_{final}}\] \[\pi {{\operatorname{r}}^{2}}_{\operatorname{o}}{{\ell }_{\operatorname{o}}}={{\pi }^{2}}_{2}n{{\ell }_{\operatorname{o}}}\] \[{{r}^{2}}_{2}=\frac{{{\operatorname{r}}^{2}}_{\operatorname{o}}}{n}\] \[{{\operatorname{R}}_{o}}=\rho \frac{{{\ell }_{\operatorname{o}}}}{\pi {{\operatorname{r}}^{2}}_{o}}\]                   ?(1) \[\operatorname{R}''=\rho \frac{\operatorname{n}{{\ell }_{\operatorname{o}}}}{\pi {{\operatorname{r}}^{2}}_{2}}\] By (1) & (2) \[\operatorname{R}''={{n}^{2}}{{R}_{o}}\]


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