Energy and Power Signals Mastery Quiz Quiz

Explore the differences between energy and power signals, common examples, and fundamental signal characteristics with these medium-difficulty questions. Enhance your understanding of signal theory for electrical engineering and related fields with key concepts about energy, power, and their criteria.

1. Identifying Energy and Power Signals

   Which of the following is an example of an energy signal based on its properties over time?

   1. A finite duration pulse of voltage
   2. A periodic triangular waveform
   3. A continuous sinusoidal voltage
   4. A constant DC voltage source

   Explanation: A finite duration pulse of voltage is an energy signal because it has nonzero energy but zero average power over infinite time. In contrast, a continuous sinusoidal voltage, constant DC voltage source, and periodic triangular waveform all have nonzero average power and infinite energy, making them power signals. Choosing these alternatives confuses periodicity or duration with energy/power classification.

2. Signal Classification Criteria

   What mathematical condition must a signal x(t) satisfy to be classified as a power signal?

   1. It must have an average power of zero
   2. It must have finite and nonzero average power
   3. It must have zero energy
   4. It must exist only for a finite time interval

   Explanation: Power signals are characterized by a finite, nonzero average power, even if their energy is infinite. Signal energy being zero does not classify it as a power signal. Existence over a finite time interval often leads to an energy signal, not power. An average power of zero would not make it a power signal.

3. Calculating Energy of a Signal

   Given the signal x(t) = 3 for 0 ≤ t ≤ 2 and zero elsewhere, what is its total energy?

   1. 12
   2. 6
   3. 18
   4. 9

   Explanation: The energy of a signal is the integral of |x(t)| squared over all time. Here, |3|^2 x (2 - 0) = 9 x 2 = 18. The option 6 could result from squaring before multiplying the interval incorrectly, 9 ignores the duration, and 12 misapplies either the value or the interval length.

4. Power of a Periodic Signal

   What is the average power of the discrete-time signal x[n] = (-1)^n, which alternates between 1 and -1 for all integer values of n?

   1. 1
   2. -1
   3. 0.5
   4. 0

   Explanation: The signal x[n] = (-1)^n always has a magnitude of 1, so squaring it over any period yields an average of 1. Choosing 0.5 could result from incorrect period averaging, -1 is invalid as power cannot be negative, and 0 confuses with signals that are mostly zero.

5. Energy and Power Signal Exclusivity

   Is it possible for a signal to be both an energy signal and a power signal simultaneously?

   1. No, a signal cannot be both
   2. Yes, if the time interval is finite
   3. Yes, if the signal is a constant
   4. Yes, for certain periodic signals

   Explanation: By definition, energy and power signals are mutually exclusive. A signal with finite nonzero energy cannot have nonzero finite power when considered over all time, and vice versa. Options referencing periodic or constant signals generally refer to power signals, while a finite time interval only applies to energy signals.