Discussion in 'Electronics Homework Help' started by bhuvanesh, Feb 23, 2015.

1. bhuvanesh

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Aug 29, 2013
in general we are checking whether the signal is power signal or energy signal. What is the use of finding whether the signal is power or energy signal. Do we have any special characteristics for energy and power signal that will be usefull for further analyses.In a nutshell WHY DO WE WANT CARE THE SIGNAL IS POWER OR ENERGY .Thank you in advance

2. (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
I'm not sure that assertion is correct.

It is a little confused because energy and power are related -- do you know the difference?

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3. (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Are you talking about a signal which has a zero vs non-zero average power?

And please don't start three threads for what is essentially one question.

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4. bhuvanesh

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Aug 29, 2013
i know the difference in general.why we have distinguished signal as power and energy signal.where we use this power and energy signals

5. KrisBlueNZSadly passed away in 2015

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I don't think you do. Can you explain what you think the difference is?

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6. bhuvanesh

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Aug 29, 2013
energy is the ability to do something and power is the energy delivered in unit time

7. KrisBlueNZSadly passed away in 2015

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OK, and what is the difference between an "energy signal" and a "power signal"?

BTW do not start any other threads on this subject.

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8. bhuvanesh

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Aug 29, 2013
Okay sorry for that. That is my problem, in electrical circuits we use power and energy terms often in many things like how much energy is dissipated in energy , so on and so forth but how do we use power signals and energy signals in signals and systems.

9. Harald KappModeratorModerator

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Nov 17, 2011
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10. bhuvanesh

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Aug 29, 2013
sine is power and u(t)-u(t-1) is energy signal(a periodic signal are energy signal)

11. Harald KappModeratorModerator

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Nov 17, 2011
This makes no sense. A sine signal is also periodic and by your definition therefore an energy signal.

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12. bhuvanesh

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Aug 29, 2013
Take a keen look of what i have said " periodic signals are power signal and aperiodic signal(non-periodic signals) are energy signals.

power signal

if a signal have constant power mean it lost some energy if a signal have no power i.e P=0(energy signal) it mean there is no energy is lost since its not going to have for too much period(non periodic)

sine signal(current) through resistor dissipate its energy as heat but a periodic signal does not cause any energy dissipation

Am i making any sense now?

13. Harald KappModeratorModerator

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Nov 17, 2011
I'm sorry, this is what your post looks like on my screen:

As you can see, there is a space between "a" and "periodic", so I read " a periodic" instead of "aperiodic".

I still do not understand your explanation:
You need to be careful when typing, here again it reads "a periodic", not "aperiodic". Also, the statement is incorrect. An aperiodic signal also can dissipate energy. Take for example a battery operated torch. Clearly the signal is aperiodic: You turn the torch on and when the battery is exhasted, the torch turns off. There is no periodicty involved. Still the lamp has dissipated lots of energy for shining a light and, as a side effect, heating the lamp.

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14. bhuvanesh

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Aug 29, 2013
wow interesting ,first time ever i am arguing confidently with people having high rating.okay let change the perspective

" all periodic signals are power signals but all power signals need not to be periodic signal".This is very famous statement ,you must have heard it. In that case step signal is only signal which is power signal but still its aperiodic.

you know very well that voltage discharged from batter is step signal and its again power signal.so its dissipates the power .Now i concluded i think

yes there is no periodicity involved but we can take whatever the period we wan it to be,cant we(this is just what i think).so it become periodic

15. Harald KappModeratorModerator

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Not famous enough for Google, nor have I ever heard it before, sorry.

16. KrisBlueNZSadly passed away in 2015

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Who said it? And can you link to where it appears?

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Aug 29, 2013
18. (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010

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19. Harald KappModeratorModerator

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Nov 17, 2011
Good find, Steve.

What is stated there makes sense if you take into consideration signals of infinite duration. I don't know what's the use for this assumption, but then again I'm not that deep into signal theory.

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