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When the magnetic flux linked with the area enclosed by a circuit changes with time, emfs and currents are induced. This electromagnetic induction has some practical consequences.
An electric current i flowing in a circuit produces a magnetic field and hence a magnetic flux Φ through the circuit. The ratio of the magnetic flux to the current is called the inductance, or more accurately self-inductance of the circuit. The quantitative definition of the inductance in SI units is given by,
In the above definition, the magnetic flux Φ is that caused by the current flowing through the circuit concerned. However, there may be contributions from other circuits. Let us consider two circuits C1 and C2 carrying the currents i1 and i2. The magnetic fluxes Φ1 and Φ2 in C1 and C2, respectively, are given by
According to the above definition, L11 and L22 are the self-inductances of C1 and C2 respectively. It can be shown that the other two coefficients are equal and L12 = L21 = M, where M is called the mutual inductance of the pair of circuits.
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Electromagnetism