Why transformer action can take place in DC and ac circuit?

Answer 1

First understand that every electrical conductor (wire) with current flow through it will produce an invisible magnetic field around it. This field is directly proportional to the magnitude of current flowing. Second (and inversely) realize that any conductor moving through a magnetic field will produce a voltage, And if provided with a complete circuit (a path to flow in) will result in current flow in that conductor. The movement can be from the conductor moving, or from the magnetic field moving, as long as there is 'relative motion' between the conductor and the magnetic field. In short, a conductor with current flow produces a magnetic field , a conductor and a magnetic field with relative motion between them produces current flow. (This is also the basis for how a motor works) AC means 'Alternating Current'! The current flow moves in one direction along a conductor, then reverses to zero and to equal magnitude in the opposite direction. Each time this current changes direction it produces a magnetic field, as it returns to zero the field collapses. As the current builds in the opposite direction the magnetic field builds again. In an AC transformer circuit, two conductors are placed in close proximity to each other and an alternating current is applied to the first conductor. This alternating current causes a magnetic field to build around the conductor, then collapse, build again in the opposite polarity and so on. This expanding and collapsing magnetic field creates relative motion between the field and the second conductor which then produces current flow of its own. This is called "transformer Action". In steady state DC circuits, the magnetic field is constant and there is normally no relative motion, therefore no "transformer action". There is however still a relative motion created when the circuit is first energized, and when it is de-energized. This collapsing field is how the ignition coil in your car works. In the simplest form, contacts (points) were opened by a cam, the open contacts de-energized the first conductor (the 12VDC primary). The resulting collapsing field cut across the secondary conductors. Because these conductors were wound into many turns or "coils" it actually multiplies the effect producing a high voltage in the secondary (connected to the ignition wires). This produced a voltage and current strong enough to jump across the gap of a spark plug. And, Yes Virginia, there is such a thing as a DC transformer.