Which coil of a transformer is to which the supply voltage is connected?

In a transformer, the primary coil is the coil to which the supply voltage is connected. This is vital to the operation of the transformer, as the primary coil creates a magnetic field when an alternating current (AC) flows through it. This magnetic field induces a voltage in the secondary coil due to electromagnetic induction, allowing for the transformation of voltage levels between the two coils.

The primary coil is responsible for receiving electrical energy from the source and is essential for initiating the process that allows the transformer to step up or step down voltage as needed for various applications. In contrast, the secondary coil is where the transformed voltage is delivered to the load.

Understanding the role of the primary coil clarifies why it is the point of connection for the supply voltage; it is the source of the energy that the transformer modifies and distributes.