# Electronics - Transformers - Discussion

Discussion Forum : Transformers - General Questions (Q.No. 3)
3.
The coefficient of coupling between two coils is 0.45. The first coil has an inductance of 75 mH and the second coil has an inductance of 105 mH. What is the mutual inductance between the coils?
3.54 mH
7.88 mH
39.9 mH
189.3 mH
Explanation:
No answer description is available. Let's discuss.
Discussion:
11 comments Page 1 of 2.

Sukruth said:   6 years ago
M = K * √(L1*L2).

Mega.k said:   7 years ago
Mutual inductance(M)=k*√(L1*L2).
Formula : K=M/√(L1*L2) for finding coefficient coupling,
So the answer is 0.45*88.74 = 39.9mH ,
M=K *√(L1*L2) for finding mutual inductance.

Bala ram said:   8 years ago
Mutual inductance formula is M = K * root(L1*L2).

Sunil sharma said:   1 decade ago
Let coefficient of coupling b/w two coils is = K.
So, K = 0.45.

First coil inductance(L1) = 75mh.
Second " " " (L2) = 105mh.

Mutual inductance(M) = k/square root of (L1*L2).

M = 0.45*square root(75*105).

M = 39.9.
(1)

M = K*square root(L1 X L2).

Coefficient of coupling (K) = 0.45
L1 = 75 mH
L2 = 105 mH
Mutual inductance M = k/(Root of L1 * L2)
M = 0.45 / Root of L1 * L2
M= 39.9 mH

M=k*(L1*L2)^(1/2)

where K=co-efficient of coupling
that is given as K=.45