Ok now please, what if its inductance?

Question

i have to figure total inductance of a 10 mH a 15 mH and a 25 mH inductor in series again i know the answer its 4.8 mH but i dunno hot to figure it

Answer 1

The answer is 10+15+25=50 mH

Answer 2

L=1/(1/10 + 1/15 + 1/25)

=4.8387mH

Answer 3

If you are sure that the three inductors are connected in series, and you know that the answer is 4.8 mH, then you are missing some information.  It is likely that at least one of the series coils is connected into the circuit with its flux mmf fields opposing the flux lines of the other two coils.  For example:

If three coils are connected in series and there's no mutually coupling between them, the total inductance, Lt = L1 + L2 + L3.

However, if there's some mutual coupling between any one or all the coils, then the total inductance is:

Lo = L1 + L2 + L3 + 3 x (k x sq. root (L1 x L2 x L3))

The mutual inductance is:  M = (Lt - Lo) / 4

Coefficient of coupling, k, = M / Sq. root (L1 x L2 x L3)

If there's series-aiding or series-opposing mutual inductance involved, your problem should have given you "k," a coeffient of coupling.

Now, if the three inductors are wired in parallel and there's no mutual coupling between them, total inductance would be:

1 / Lt = 1 / L1 + 1 / L2 + 1 / L3,

or, Lt = ((L1 x L2 x L3) /( L1 + L2 +L3))

Lt = (L1 x L2 x L3 x (1 - k^2)) / (L1 + L2 + L3 - 3) x (k x Sq. root (L1 x L2 x L3))

4.8 mH would be a reasonable answer for parallel coils.

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