Which type of transmission uses continuously varying electrical signals?

The type of transmission that uses continuously varying electrical signals is analog. Analog transmission conveys information through continuous signals that can vary in amplitude, frequency, or phase. This characteristic allows analog signals to represent a range of values, such as sound waves or light intensity, which are inherently variable in nature.

In contrast, other transmission types have different signal characteristics. For example, digital transmission uses discrete signals that represent data as binary numbers (0s and 1s), creating a distinct on-off signaling scheme rather than a continuous wave. Parallel and serial transmissions refer to the method of data transfer, where parallel transfers multiple bits simultaneously over multiple channels, whereas serial transfers bits one at a time over a single channel. However, neither of these methods defines the type of signal used in the way analog does. Therefore, the correct identification of analog as a transmission type that utilizes continuously varying signals is critical for understanding how different types of information are transmitted in communication systems.