What characterizes thermal noise?

The correct answer highlights that thermal noise is fundamentally a consequence of the random motion of electrons within a conductor that occurs due to thermal energy at a given temperature. As temperature increases, the kinetic energy of the electrons also increases, leading to greater movement and consequently more noise. This thermal noise, also referred to as Johnson-Nyquist noise, is present in all resistive components and is directly proportional to the temperature and resistance of the material. It operates independently of any external interference or applied voltage, instead arising solely from the intrinsic characteristics of the material itself. Understanding this noise is crucial for the analysis and design of electronic circuits, as it sets a lower limit on how much signal can be distinguished from the noise in communication systems.