How is binary data sent across copper cables?

Binary data is sent across copper cables primarily by changing the voltage between two ranges. In this context, each binary digit (or bit) is represented by a specific voltage level. For example, one voltage level might represent a binary "1," while another level represents a binary "0." This method is effective for encoding and transmitting digital information efficiently over short and long distances, making copper cables, such as those used in traditional telephone or data cabling, capable of carrying this type of information.

The other options involve different methods of data transmission. Altering the frequency of the signal is associated with certain types of analog transmission or modulation techniques but is not the main method for transmitting binary data over copper cables. Using electromagnetic waves pertains to wireless transmission rather than wired communication. Fiber optic conversion relates to light-based transmission and is not relevant for copper cables, which rely on electrical signals rather than optical signals.