# Signal power vs signal energy

Hi, I have trouble understanding these concepts

http://cnx.org/content/m10055/latest/

if I understand is correctly, the energy is basically a number telling us how "big" a signal is

while the power, is used for signals that don't decay, thus give us a infinite amount of energy, but still we need to find a measurement for how "big" these signals are and hence we use the concept of "signal power"

is this correct? I'm not really sure about it 100%

also what's the point of these measurements?

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ideasrule
Homework Helper
if I understand is correctly, the energy is basically a number telling us how "big" a signal is

I'm not sure this is a good way to put it. How "big" a signal is should correspond more closely to the signal amplitude, not the energy.

Maybe an example would help. Imagine a pair of purely resistive speakers that got turned on at t1 and turned off at t2. The signal is the current that we measure through the speakers, and energy would be proportional to the total amount of electricity that the speaker used.

However, energy might not be very useful. Obviously if I leave the speaker on for a longer time, it's going to use more energy, even if I'm just playing the same song over and over again. Power is the electricity used per second, and indicates how powerful the speakers are.

thanks that made it clear to me ;)