energy or power

[electronist]

what is the practical difference between a power signal and an energy signal. I know the mathematical part of integration and stuff but how would i physically distinguish between the two.
Power i understand is the product of v & i, and hence the outcome is a power signal which i can view on a scope, but since energy is area under the curve i am totally confused. could any one please clear my doubts

 

[JohnBrown]

Power is the 3 kilowatts your electric fan heater consumes. Energy is the 30 kilowatt hours you have to pay for when your daughter leaves it on overnight for ten hours.

 

[electronist]

my question is that if a signal is shown to me in abook ithen how do i say whether it is a power signal or a energy signal

 

[williB]

Energy and work are both measured in joules. Power is measured in joules per second, a unit that we call a watt.

 

[sonaiko]

my question is that if a signal is shown to me in abook ithen how do i say whether it is a power signal or a energy signal

i understand ur question.
now if a signal approches zero when time goes to infinity then it is an enrgy signal (e.x: e to the power -x)
if a signal repeates its self in a period it is most likely to be power signal. (the sin and cos).

is that enough?

 

[electronist]

do you mean that any non peridic signal is an energy signal if it approaches zero over no time limit ie infinity
Does that mean that periodic signals cannot be labelled as energy signals
Please help me out of this mess

 

[Optikon]

do you mean that any non peridic signal is an energy signal if it approaches zero over no time limit ie infinity
Does that mean that periodic signals cannot be labelled as energy signals
Please help me out of this mess

I don't think it can be generalized to periodic signals. What about (e^-t)*(sin wt) this signal decays toward zero and is periodic.

Think about the physical meaning of the integration in the definition.

 

[Oznog]

my question is that if a signal is shown to me in abook ithen how do i say whether it is a power signal or a energy signal

If you see a waveform in a book, 95% of the time it's either voltage or current. That is neither power nor energy.

Rarely will you see power graphed out, but it does have meaning in some contexts. Far more rarely will you see energy. Maybe you'd see it in regards to battery discharge, but even then it would be amp-hrs and not energy.

But, silly observation- any graph should list the units, so just read them. Power is in watts. Energy is in watt-hrs, kilowatt-hrs, Joules.

 

[Optikon]

my question is that if a signal is shown to me in abook ithen how do i say whether it is a power signal or a energy signal

If you see a waveform in a book, 95% of the time it's either voltage or current. That is neither power nor energy.

Rarely will you see power graphed out, but it does have meaning in some contexts. Far more rarely will you see energy. Maybe you'd see it in regards to battery discharge, but even then it would be amp-hrs and not energy.

But, silly observation- any graph should list the units, so just read them. Power is in watts. Energy is in watt-hrs, kilowatt-hrs, Joules.

I think the author was referring to what are defined as "energy" or "power" type signals from a signal processing point of view. These definitions are without regard to units. So, what we're talking about here are not actually energy and power waveforms (I think!) but rather, given a signal, how can one tell if it would be classified as an energy type or power type from a signal analysis definition. In otherwords, how can one clssify the signal based on how it looks so as to avoid performing the math integral.

Original author please correct me if I am wrong!

 

[krishnakanth]

do you mean that any non peridic signal is an energy signal if it approaches zero over no time limit ie infinity
Does that mean that periodic signals cannot be labelled as energy signals
Please help me out of this mess

I hope u understand this.

Power Signals:
These signals exist for infinite time .
The energy of the power signal is infinite.
Practical periodic signals are power signals.
e.g: a pulse train.

Energy signals:
Non periodic signals are energy signals.
These signals are time limited.
e.g: a single rectangular pulse

 

[electronist]

Thank You opticon for reading my mind and putting it down in a perfect sense.
What the hell is energy of power signal and power of energy signal when one is the derivative of the other?
as Ive already said before ive read books ranging from Simon haykins to Robort MJ, but this topic still confuses me

 

[krishnakanth]

Thank You opticon for reading my mind and putting it down in a perfect sense.
What the hell is energy of power signal and power of energy signal when one is the derivative of the other?
as Ive already said before ive read books ranging from Simon haykins to Robort MJ, but this topic still confuses me

ill put very simply.
energy signals and power sgnals have nothing to do with what their name suggests.

there is no specific signal called "energy signal or power signal".
consider a signal if this signal has finite energy it is called an energy signal.

if it has finite power it is called power signal.

i think you know by the formulas how to calculate power and enrgy of given signals i.e integration and stuff. how to idetif the given signal whether its energy or power signal i think it has already been answered.
:idea:

i know all this cause i have a subject called signal & systems.if u hv any other doubts ill be very glad to answer.(i have an exam on this day after tommorrow).