This Equation calculates the Core Geometry, a commonly used constant that characterizes a transformer.  The core geometry would often be used in the design of transformers.  The core geometry is expressed in units of `cm^5`.

A transformer is used to step up or step down AC voltage by using the principle of magnetic induction between the transformer's multiple wire windings.   

Inputs

• `rho` - resistivity (`Omega` * cm) - for copper wire an estimated value is used for the default of 1.724E6 `Omega` * cm)
• L - Inductance (Henrys)
• `I_max` - Peak Winding current (amps)
• `B_max` - Maximum flux density in the core (Tesla)
• `R` - Winding Resistance (`Omega`)
• `K_u` - Winding Fill Factor (unitless)

Notes

The core size and shape of the core have a lot to do with the current, power, and frequency of the transformer.  The transformer designer also has to consider power loss in the core.  The size of the core therefore depends on the power of the transformer and the expected power loss in the core.  Once the core type, size, and shape are selected the core geometry and its component geometries can be calculated.