NEET Sample Paper NEET Sample Test Paper-4

  • question_answer
    The masses of the three wires of copper, are in the ratio \[1:3:\text{ }5\] and their length, are in ratio \[5:3:-1\] the ratio of their electrical resistances:

    A)  \[1:3:5\]                      

    B)  \[5:3:1\]

    C)  \[\text{1}:15:125\]                    

    D)  \[125:15:1\]

    Correct Answer: D

    Solution :

    As  \[R=\frac{\rho l}{A}=\frac{\rho {{l}^{2}}}{A\,I}=\frac{\rho {{l}^{2}}}{V}=\frac{\rho {{l}^{2}}}{m/d}\] \[\Rightarrow \]            \[R=\frac{\rho d{{l}^{2}}}{m}\] or \[R\propto \frac{{{l}^{2}}}{m}\] \[\Rightarrow \]   \[{{R}_{1}}:{{R}_{2}}:{{R}_{3}}=\frac{l_{1}^{2}}{{{m}_{1}}}:\frac{l_{2}^{2}}{{{m}_{2}}}:\frac{l_{3}^{2}}{{{m}_{3}}}\]             \[=\frac{25}{1}:\frac{9}{3}:\frac{1}{5}=125:15:1\]


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