Verified Solution • 2025–26 Session moderate

QJEEM19Phb5b8: JEE Main 2019 Physics - Class 12 JEEM19Phb5b8 Solution: There are two long co-axial solenoids of same length . The…

There are two long co-axial solenoids of same length ll . The inner and outer coils have radii r1 and r2 and number of turns per unit length n1 and n2, respectively. The ratio of mutual inductance to the self - inductance of the inner-coil is :

Multiple Choice Options

  • A n2n1.r22r12{{{n_2}} \over {{n_1}}}.{{{r_2}^2} \over {{r_1}^2}}
  • B n2n1{{{n_2}} \over {{n_1}}}
  • C n1n2{{{n_1}} \over {{n_2}}}
  • D n2n1.r1r2{{{n_2}} \over {{n_1}}}.{{{r_1}} \over {{r_2}}}

Step-by-Step Verified Solution

M=μ0 n1 n2 πr12M = {\mu _0}\,{n_1}\,{n_2}\,\pi r_1^2

L=μ0 n12 πr12L = {\mu _0}\,n_1^2\,\pi r_1^2

⇒  ML=n2n1\Rightarrow \,\,{M \over L} = {{{n_2}} \over {{n_1}}}

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