Summarizing Transformers


  • Transformers use induction to transform voltages from one value to another.
  • For a transformer, the voltages across the primary and secondary coils are related by


    where \({V}_{\text{p}}\) and \({V}_{\text{s}}\) are the voltages across primary and secondary coils having \({N}_{\text{p}}\) and \({N}_{\text{s}}\) turns.

  • The currents \({I}_{\text{p}}\) and \({I}_{\text{s}}\) in the primary and secondary coils are related by \(\cfrac{{I}_{\text{s}}}{{I}_{\text{p}}}=\cfrac{{N}_{\text{p}}}{{N}_{\text{s}}}\).
  • A step-up transformer increases voltage and decreases current, whereas a step-down transformer decreases voltage and increases current.



a device that transforms voltages from one value to another using induction

transformer equation

the equation showing that the ratio of the secondary to primary voltages in a transformer equals the ratio of the number of loops in their coils; \(\cfrac{{V}_{\text{s}}}{{V}_{\text{p}}}=\cfrac{{N}_{\text{s}}}{{N}_{\text{p}}}\)

step-up transformer

a transformer that increases voltage

step-down transformer

a transformer that decreases voltage

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