Give two definitions of mutual inductance, give its units and write factors on which its value depends.
The flux $\Phi_{2}$ linked with the coil-$2$ when current through coil-$1$ is $\mathrm{I}_{1}$ is $\Phi_{2}=\mathrm{M}_{21} \mathrm{I}_{1}$.
Taking $\mathrm{I}_{1}=1$ unit, $\Phi_{2}=\mathrm{M}_{21}$. Thus,
"The magnetic flux linked with one of the coils of a system of two coils per unit current passing through the other coil is called mutual inductance of the system formed by the two coils."
Mutual emf produced in coil-2 is given by,
$\varepsilon_{2}=-\mathrm{M}_{21} \frac{d \mathrm{I}_{1}}{d t}$
When $\frac{d \mathrm{I}_{1}}{d t}=1$ unit in the equation $(2)$,
$\varepsilon_{2}=\mathrm{M}_{21}$. Thus,
"The mutual emf generated in one of the two coils due to a unit rate of change of current in the other coil is called mutual inductance of the system of two coils".
The unit of mutual inductance is
$\mathrm{WbA}^{-1}=\frac{\mathrm{V} \cdot s}{\mathrm{~A}}=$ henry $(\mathrm{H})$
The value of mutual inductance of a system of two coils depends upon :
$(1)$ Shape of coils
$(2)$ Size of coils
$(3)$ Number of turns in two coils
$(4)$ Distance between them
$(5)$ Angle of mutual inclination
$(6)$ The material on which they are wound
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There are two coils $\mathrm{A}$ and $\mathrm{B}$ separated by some distance. If a current of $2\mathrm{A}$ flows through $\mathrm{A}$, a magnetic flux of $10^{-2}\mathrm{Wb}$ passes through $\mathrm{B}$ ( no current through $\mathrm{B}$ ). If no current passes through $\mathrm{A}$ and a current of $1\mathrm{A}$ passes through $\mathrm{B}$, what is the flux through $\mathrm{A}$ ?