# Summarizing Transformers

## Summary

• 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

$$\cfrac{{V}_{\text{s}}}{{V}_{\text{p}}}=\cfrac{{N}_{\text{s}}}{{N}_{\text{p}}}\text{,}$$

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.

## Glossary

### transformer

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