Transformers

Coils of wire can be used to induce current in other coils of wire. Induction Coils of wire can be used to induce current in other coils of wire. Current will only be induced when there is a changing magnetic field. This means that in order for a coil of wire to induce a current the magnetic field around the coil must be changing. This is the case where AC is used. Since AC changes direction constantly, the magnetic field around a coil with AC also changes constantly.

Primary and Secondary The changing magnetic field of the primary coil induces a current in the secondary coil. This is the basis of a transformer.

Transformers use coils to change the amount of current and voltage. Transformers can “step up” or “step down” voltage by varying the number of loops in the two coils. Remember Faraday’s Law of Induction states that the induced voltage is proportional to the number of loops in a coil. Thus a larger secondary coil will have more induced voltage while a smaller secondary coil will have less induced voltage.

Since the time will be the same for both coils Energy is Conserved This means that Remember the Energy = Power * time. Thus if the energy is the same (assuming an ideal transformer) and the time is the same then the power must be the same. In the equation above P1 is the power of the primary coil and P2 is the power of the secondary coil. Since the time will be the same for both coils

Transformer Equation This equation indicates that the ratio of voltage to loops is the same for both the primary and secondary coils. V is the voltage, n is the number of loops and the subscripts are 1 for primary and 2 for secondary.

Current Note that this equation indicates that the change in voltage from a transformer is accompanied by a change in current. In a step up transformer the voltage increases and the current decreases. In a step down transformer the voltage decreases and the current increases.

Power Transmission www.howstuffworks.com A power grid consists of a power plant that generates the electricity, high voltage transmission lines, substations and other transmission lines and transformers. www.howstuffworks.com

Power Plant A step up transformer is used at the plant to increase the voltage and decrease the current. Lower current means less power loss due to heating of the the transmission lines.

Substation A substation is a step down transformer that reduces the voltage and increases the current. Substations serve large areas of cities and towns.

Drum Transformers Each house or every other house has a drum transformer that steps down the voltage to the 240 V that each house needs.