TRANSFORMERS

Transformers are usually AC activated devices.  The change in signal across the Inductors causes a Counter EMF which is voltage is the opposite polarity.

Transformer transfer voltage from one circuit to another.

The greater the amount of secondary windings in the coil, then the greater the amount of resistance and hence lower the current.

A 20:1 is a step down transformer
A 1:10 is a step up transfomer (volts)

So the 20:1 transformer would produce more current and less voltage compared to its primary windings (or circuit), as there is less amount of windings, hence less resistance and more current can flow. 
Note however, that the power is the same before the transfer of voltage (via th transformer)
This is the inverse for the 1:20 transformer.

There are different types of Transformers:  

Audio Transformers are used because of their effeciency.
Impedance Matching Transformers are used for maximum power output to the load (e.g speaker)
Power Transformers are used to supply appropriate voltages to components e.g. the PSU in a PC.

If the winding of a transformer has a large diameter wire, then its windings carry high current and low voltage.  The opposite is true - where a small diameter wire carries high voltage but low current.