Explain why a transformer doesn't work with DC.

A transformer consists of two coils of wire, called the primary and secondary windings, wrapped around a common ferromagnetic core (usually iron). The primary winding is connected to an input voltage source, while the secondary winding is connected to the output. When an alternating current (AC) is applied to the primary winding, it creates a continually changing magnetic field around the primary coil and inside the core. This varying magnetic field induces an electromotive force (EMF) in the secondary winding, creating an output voltage. The voltage transformation ratio depends on the number of turns in the primary and secondary windings.

An alternating current (AC) continuously changes its direction and magnitude, causing the magnetic field around the primary coil to vary. This changing magnetic field is necessary for inducing EMF in the secondary coil via electromagnetic induction. On the other hand, direct current (DC) maintains a constant direction and magnitude, which means that once the current reaches its maximum value, the magnetic field around the primary coil and within the core becomes constant and does not change over time.

If a DC voltage is applied to the primary winding of a transformer, there will be no continually changing magnetic field induced in the core. Since electromagnetic induction relies on a varying magnetic field to generate EMF in the secondary coil, a constant magnetic field will not produce any voltage across the secondary winding. Therefore, the transformer would not work in transferring electrical energy from the primary to the secondary winding. Additionally, when DC voltage is applied to the primary winding, the constant current can cause the core to saturate, leading to overheating and potentially damaging the transformer. Furthermore, the inrush current during the initial connection of the DC voltage can be much higher than the rated current of the transformer, causing excessive stress and even failure of the transformer.