If a current I₁ flows in C₁ , the magnetic flux B₁ will be created part of which will be linked to C₂ as shown in Figure 4.10.

...................................(4.48)

In a linear medium, is proportional to I ₁. Therefore, we can write

        ...................................(4.49)

where L₁₂ is the mutual inductance. For a more general case, if C₂ has N₂ turns then

        ...................................(4.50)

and     

or           ...................................(4.51)