Step-up transformers
Reversing the situation, we can make a step-up transformer that boosts a low voltage into a high one:
This time, we have more turns on the secondary coil than the primary. It's still true that:
Secondary voltage ÷ Primary voltage = Number of turns in secondary ÷ Number of turns in primary
and
Secondary current ÷ Primary current = Number of turns in primary ÷ Number of turns in secondary
In a step-up transformer, we use more turns in the secondary than in the primary to get a bigger secondary voltage and a smaller secondary current.
Considering both step-down and step-up transformers, you can see it's a general rule that the coil with the most turns has the highest voltage, while the coil with the fewest turns has the highest current.
