Final answer:
A transformer with a one-to-one turn ratio does not change the voltage; it maintains the same voltage level from the primary to the secondary winding and is typically used for isolation.
Step-by-step explanation:
When examining what a transformer with a one-to-one turn ratio does to voltage, it's essential to understand the basics of the transformer equation. This equation states that the ratio of the secondary voltage to the primary voltage in a transformer equals the ratio of the number of turns in the secondary coil to the number of turns in the primary coil. When the turn ratio is one-to-one, this means that the number of turns in the secondary coil is equal to the number of turns in the primary coil.
In such a case, a transformer with a one-to-one turn ratio will neither increase nor decrease the voltage. Instead, it maintains constant voltage from the primary side to the secondary side. This type of transformer is often used for isolation purposes rather than for changing voltage levels.