• # question_answer The total number of turns and cross-section area in a solenoid is fixed. However, its length L is varied by adjusting the separation between windings. The inductance of solenoid will be proportional to: [JEE Main 9-4-2019 Morning] A) $1/{{L}^{2}}$B)               $1/L$C) $L$                            D) ${{L}^{2}}$

$\phi =NBA=LI$           $N{{\mu }_{0}}nI\pi {{R}^{2}}=LI$ $N{{\mu }_{0}}\frac{N}{\ell }I\pi {{R}^{2}}=LI$ $N\And R$constant self inductance$(L)\propto \frac{1}{\ell }\propto \frac{1}{length}$ Option