Answer:
Time interval for which magnetic field reduced to ZERO is given as
[tex]t = \frac{NB_0\pi a^2}{RI}[/tex]
Explanation:
As we know that the flux linked with one coil is given as
[tex]\phi = B_0 A[/tex]
[tex]\phi = B_0(\pi a^2)[/tex]
now total flux of all coils is given as
[tex]\phi = NB_0\pi a^2[/tex]
now let say the flux is reduced to ZERO after time "t"
so as per Faraday's law EMF induced in the coil is given as
[tex]EMF = \frac{NB_0\pi a^2 - 0}{t}[/tex]
now the current in the coil is given as
[tex]I = \frac{EMF}{R}[/tex]
[tex]I = \frac{NB_0\pi a^2}{Rt}[/tex]
so the time interval is given as
[tex]t = \frac{NB_0\pi a^2}{RI}[/tex]