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Heating Effect Of Current...

by app
Tags: current, effect, heating
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Aug5-06, 08:31 AM
P: 46
INTRODUCTION:Here is a problem on "Heating Effect Of Current".I can't understand a part of it.
EXACT PROBLEM: "A battery of emf E and internal resistance r is supplying current to an external resistance R.(a)Show that the power dissipated in R will be maximum when R=r.(b)What is the maximum power?(c)What would happen if the battery is shorted?"
WHAT MY BRAIN SUGGESTED:(a)The current in the circuit is i=E/(R+r).Power dissipated is P=(i^2)r.Now putting the value of i, we find that P will be maximum when denominator is minimum,i.e. (R-r)^2 is 0. So, R=r.
(b)Putting r in place of R in the power equation, we get maximum power as (E^2)/4r.
(c) ***ERROR***The word "shorted" is not yet registered in the PHYSICS part of my brain .BRAIN CANNOT SUGGEST ANYTHING.SORRY.
CONFUSION:What does "battery is shorted" mean?And what would happen if the battery is shorted?
CONCLUSION:Physics Forums say that it is necessary to show that one has tried a particular problem in order to be answered.But what can one do if he cannot understand the meaning of a term?(I don't know what exactly "shorted" is).How will i prove that i've really tried part (c)?Nevertheless, i've tried to show that i know the other things of "Heating Effect Of Current".If you still don't believe me i have nothing to say. But if you do help me, thank you in advance.
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Aug5-06, 09:07 AM
P: 21
Hello, I think shorted implies a short circuit, and the heating effect of current is joule heating--Joule's Law.
Doc Al
Aug5-06, 09:16 AM
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P: 41,440
"The battery is shorted" means that instead of connecting an external resistance across the battery terminals you connect a plain conducting wire across them. Assume the wire has zero resistance and thus creates the so-called "short circuit".

Aug5-06, 09:19 AM
P: 46
Smile Heating Effect Of Current...

so in this case, what would happen if the battery is shorted. plesae explain. it is the first time i'm coming across short circuit problems. thanks.
Doc Al
Aug5-06, 09:25 AM
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P: 41,440
Just redo your analysis, only this time have R = 0.
Aug5-06, 09:43 AM
P: 46
thanks a lot.

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