BHU PMT BHU PMT (Mains) Solved Paper-2009

  • question_answer
    A toroidal solenoid with an air core has an average radius of 15 cm, area of cross-section 12cm and 1200 turns. Ignoring the field variation across the cross-section of the toroid, the self-inductance of the toroid is

    A)  4.6 mH                

    B)  6.9 mH

    C)  2.3 mH                

    D)  9.2 mH

    Correct Answer: C

    Solution :

                     For a solenoid                 \[B={{\mu }_{0}}nI\]                 where     \[n=\frac{N}{2\pi r}\]                 \[\Rightarrow \]               \[B=\frac{{{\mu }_{0}}NI}{2\pi r}\]                 Flux linked with the solenoid is                 \[\phi =NBA\]                 \[\Rightarrow \] \[\phi =\frac{{{\mu }_{0}}{{N}^{2}}A}{2\pi r}\]                 \[\Rightarrow \] \[L=\frac{\phi }{I}=\frac{{{\mu }_{0}}{{N}^{2}}A}{2\pi r}\]                 \[\Rightarrow \] \[L=2.3\times {{10}^{-3}}H\]


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