Final answer:
The statement about dedicated circuit networks using internet infrastructure is not necessarily true; dedicated circuits may use private networks as well. High-voltage wires are not insulated; they are held up by insulating connectors. Refraction in fiber optics is true, aiding signal transmission, and voltage in a circuit diagram is not constant throughout.
Step-by-step explanation:
The statement in question refers to a dedicated circuit network, which is a communication technique used for data communication. Its main characteristic is the direct and constant link established between two points for the duration of the connection. Contrary to the proposition in the statement, a dedicated circuit network does not necessarily use the internet's infrastructure to provide communication between cities. Instead, dedicated circuits, especially in a Wide Area Network (WAN) context, can either use public infrastructure such as the internet or private networking facilities that do not rely on the internet at all.
As for the second part of the question regarding high-voltage wires, the statement that they are wrapped in an insulating material is false. These wires are typically bare and are held aloft by insulating connectors due to the high costs and impracticality of insulating such high-voltage lines.
In the context of fiber optic cables, refraction is indeed a useful principle for transmitting signals. The phenomenon of refraction, which is the bending of light as it passes from one medium to another with a different density, is essential in guiding light through the fiber optic cable, thus making the statement true.
Regarding the concept of voltage in a circuit diagram, it is false to assume that the voltage is the same at every point in a given wire. Voltage, by definition, is the electric potential difference between two points; hence it changes along a circuit depending on the components connected.