# What are the conditions for a signal to be an energy signal and a power signal?

I know how to find the power and the energy of a signal. What I have a problem with is knowing whether a signal is an energy signal or a power signal.

According to my teacher, a signal is a power signal if its power is finite (less than infinity) and non-zero and a signal is an energy signal if its energy is finite (less than infinity). What he does not specify is what happens if the energy of a signal is 0 such as in the case of the signal x(t) = 0.

The energy is obviously 0. Is this signal considered an energy signal or the signal x(t) is not considered a signal at all since its zero?

Furthermore, is it possible for a signal to be neither a power signal nor an energy signal?

Thank you.

I don't think that this line of thought is going to help you much.

signal [sig-nl]
Electronics. an electrical quantity or effect, as current, voltage, or electromagnetic waves, that can be varied in such a way as to convey information. Source: Dictionary.com.

In most cases some power will be required to pass the information but that is inherent in the way electronics works and it doesn't mean that power is a signal.

In contrast power suggests providing energy to a device with no information transmitted.

The energy is obviously 0. Is this signal considered an energy signal or the signal x(t) is not considered a signal at all since its zero?

I would think that zero indicates a lack of power or signal. It's nothing.

Furthermore, is it possible for a signal to be neither a power signal nor an energy signal?

We're back to the definitions again. If it's a signal then it's a signal.