Which statement best describes a power signal as given?

Which statement best describes a power signal as given?

• A. Finite energy
• B. Periodic signal
• C. Infinite energy
• D. Random process

Answer: (B)

Power signals have finite, nonzero average power when observed over long time intervals. For a periodic signal, this is exactly the case: because the signal repeats every T0, the energy it contains in each period is a fixed finite amount, say E0. If you look over a long window, the total energy scales with the number of periods, while the time window scales with the same number of periods, so the average power becomes E0 divided by T0. This yields a finite, nonzero value, which is why periodic signals are classic examples of power signals.

In contrast, energy signals have finite total energy but zero average power when observed for a long time, since energy is confined to a finite amount of time. Signals with infinite energy do not have finite average power and thus aren’t power signals. Random processes can be analyzed in terms of average power as well, but the essential idea here is that the repeating nature of a periodic signal guarantees a finite, nonzero average power, making it the best description among the options.