Which statement about energy signals is true?

• A. An energy signal has zero energy.
• B. It has finite energy and zero average power.
• C. The energy of a signal is always finite.
• D. An energy signal has infinite energy and nonzero average power.

Answer: (B)

Energy signals are those for which the total energy is finite, measured by E = ∫{-∞}^{∞} |x(t)|^2 dt. Because this integral converges to a finite value, the average power, defined as P = lim{T→∞} (1/2T) ∫_{-T}^{T} |x(t)|^2 dt, must go to zero—the numerator approaches a finite energy E while the time interval grows without bound. So an energy signal has finite energy and zero average power. This contrasts with signals like continuous sinusoids, which have infinite energy over all time but a nonzero finite average power, making them power signals. Thus the true statement is that an energy signal has finite energy and zero average power.