Two coaxial solenoids 1 and 2 of the same length are set so that one is inside the other. The number of turns per unit length are n1 and  n2. The currents  i1 and  i2 are flowing in opposite directions. The magnetic field inside the inner coil is zero. This is possible when

 

  • Option 1)

     i1≠i2    and    n1=n2

     

  • Option 2)

    i1=i2    and     n1≠n2

     

  • Option 3)

     i1=i2    and     n1=n2

     

  • Option 4)

     i1n1=i2n2

     

 

Answers (1)

As we learnt in 

Magnetic field due to Infinite length solenoid -

\alpha =\beta =\frac{\pi }{2}

 Bin=\mu _{o}ni

- wherein

Point is well inside the solenoid 

 

B_{solenoid}=\mu_o ni

For B_{net}=0    

\Rightarrow \left | \vec{B_1} \right |=\left | \vec{B_2} \right |

\Rightarrow \mu_{0}n_{1}i_{1}=\mu_{0}n_{2}i_{2}

\Rightarrow n_1i_1= n_2i_2 

 


Option 1)

 i1≠i2    and    n1=n2

 

incorrect

Option 2)

i1=i2    and     n1≠n2

 

incorrect

Option 3)

 i1=i2    and     n1=n2

 

correct

Option 4)

 i1n1=i2n2

 

incorrect

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