Final answer:
Impedance is the total opposition to the flow of current in a transformer, which includes both resistance and inductive reactance. Isolation transformers are used to increase resistance and prevent complete circuits in safety applications.
Step-by-step explanation:
The total opposition to the flow of current in a transformer is known as impedance, a term that extends beyond simple resistance to include other factors like inductive reactance and the phase angle between the voltage and the current in the circuit. An example of a device that creates a significant resistance to ensure safety is the isolation transformer. Isolation transformers are designed to provide a large resistance between a voltage source and a device to prevent a complete circuit and to protect against electric shock, as there is not a complete circuit that allows for current to flow through a person who might come into contact with one of the output wires.