Two coils of self-inductance \(2~\text{mH}\) and \(8~\text{mH}\) are placed so close together that the effective flux in one coil is completely linked with the other. The mutual inductance between these coils is:
1. \(10~\text{mH}\)
2. \(6~\text{mH}\)
3. \(4~\text{mH}\)
4. \(16~\text{mH}\)

Two coils have a mutual inductance \(0.005\) H. The current changes in the first coil according to equation \(I=I_{0}\sin\omega t\) where \(I_{0}=2\) A and \(\omega=100\pi \) rad/s. The maximum value of emf in the second coil is:
1. \(4\pi\) V
2. \(3\pi\) V
3. \(2\pi\) V
4. \(\pi\) V