What formula is used to calculate the power rating of the primary winding of a transformer?

The formula to calculate the power rating of the primary winding of a transformer is derived from the relationship between voltage and current in an electrical circuit. In this context, the power rating (in volt-amperes, VA) of the primary winding is given by multiplying the primary voltage (Vprimary) by the primary current (Iprimary).

This reflects how much power the transformer can handle on the primary side, as power in an electrical system is defined as the product of voltage and current. Thus, the formula VAprimary = Vprimary * Iprimary accurately captures the power capacity of the transformer’s primary winding.

When assessing the other options, it's clear that while they may involve electrical parameters, they don't correctly represent the power rating of the transformer. For instance, adding voltage and current does not yield a meaningful power measurement, and calculating power with the secondary current or using division is not applicable in this scenario. Hence, the correct approach is to use the multiplication of primary voltage and primary current, confirming that option C is the right formula to use.