Coupling Coefficient Formula:

The correct formula to find the coupling coefficient is option 'A': k = M/sqrt(L1L2).

Explanation:

In electrical engineering, the coupling coefficient is a measure of the extent to which two coils or inductors are magnetically linked. It represents the fraction of magnetic flux produced by one coil that links with the other coil.

The coupling coefficient, denoted by 'k', can be calculated using the mutual inductance (M) and the self-inductances (L1 and L2) of the two coils. The formula for the coupling coefficient is given by:

k = M/sqrt(L1L2)

Let's break down the formula and understand its components:

Mutual Inductance (M):
Mutual inductance is a measure of the magnetic coupling between two coils. It determines how much magnetic flux produced by one coil links with the other coil. The unit of mutual inductance is Henry (H).

Self-Inductance (L1 and L2):
Self-inductance is a property of an individual coil that represents its ability to store magnetic energy when a current flows through it. It is a measure of the opposition offered by the coil to changes in current. The unit of self-inductance is also Henry (H).

Square Root (sqrt):
The square root function is used to calculate the square root of a number. In this case, it is used to find the square root of the product of the self-inductances (L1 and L2).

By dividing the mutual inductance (M) by the square root of the product of the self-inductances (L1L2), we can obtain the coupling coefficient (k). The coupling coefficient is a dimensionless quantity and ranges from 0 to 1, where 0 indicates no coupling and 1 indicates maximum coupling.

Therefore, the correct formula to find the coupling coefficient is k = M/sqrt(L1L2), as given in option 'A'.