A simple single-phase transformer consists of two conductors. When a certain amount of current (such as alternating current or pulsed direct current) passes through one of the conductors, a changing magnetic field will be generated. According to the principle of mutual inductance in electromagnetism, this changing magnetic field will cause an electric potential difference in the second conductor. If the second conductor is part of a closed circuit, then an electric current will be generated in that closed circuit. Electricity was thus transmitted. In a common transformer, the relevant conductors are coils composed of (mostly copper) wires, because the magnetic field generated by the coils is much greater than that of a straight wire. The principle is that a transformer is a device that transforms alternating voltage, alternating current and impedance. When alternating current flows through the primary coil, alternating magnetic flux is generated in the iron core (or magnetic core), inducing voltage (or current) in the secondary coil. There is a direct proportional relationship between the voltages VS and VP of the primary and secondary coils and the number of turns NS and NP of their windings.
As for the ratio of current or voltage between the two sides of the transformer, it depends on the number of turns of the coils in the circuits on both sides. The side with more turns has a higher voltage but a smaller current, and vice versa. If factors such as leakage are excluded, the voltage ratio on both sides of the transformer is equal to the ratio of the number of turns of the coils on both sides, that is, the voltage is directly proportional to the number of turns.
Therefore, the turns ratio of the primary coil and the secondary coil can be reduced or increased, thereby raising or lowering the voltage. This property of the transformer makes it an important device for voltage conversion. Moreover, excluding the factor of leakage, since the transformer adheres to these two laws, it cannot be an amplifier. If the voltages on both sides of the transformer are different, then the currents flowing through the two sides of the transformer will also be different, and the difference between the two is inversely proportional. If the current on one side of the transformer is smaller than that on the other side, the side with the smaller current will have a larger voltage. And vice versa. However, the power consumed by both sides of the transformer (that is, the product of the voltage and current values of one side) should be equal.