Electronic – Why are transformers cores made of iron and not nickel, when the relative permeability is higher for nickel

Iron is a poor conductor compared to copper so making an electromagnet from iron wire is off to a bad start. Next, an electromagnet has basically a massive air gap and this is the bit that attracts i.e. the working end of an electromagnet is the air gap. This is generally why the attractive force produced by a solenoid electromagnet has nothing to do with the permeability of the core: -

Force = \$(N\cdot I)^2\cdot 4\pi 10^{-7}\cdot \dfrac{A}{2g^2}\$

• F = Force
• I = Current
• N = Number of turns
• g = Length of the gap between the solenoid and the magnetizable metal
• A = Area

Yea dependence is there.

At the interface between two mediums : 1 and 2, the amount of reflection of EM waves for perpendicular incidence, can be described by its reflection coefficient. $$\rho = \left(\frac{\eta_1 -\eta_2}{\eta_1 +\eta_2}\right)$$ where, $$\eta_1 = \sqrt{\mu_1/\epsilon_1}$$ $$\eta_2 = \sqrt{\mu_2/\epsilon_2}$$ similarly the amount of transmission can be described corresponding transmission coefficient $$\tau = 1+\rho $$

EDIT:

The coefficients are defined in terms of amplitudes of the incident, transmitted and reflected waves.