Current Entering And Leaving Battery

  • #1

Main Question or Discussion Point

Why the current entering and leaving the battery in an elctirc circuit needs to be same??plz provide a mathematical proof for this.
thanks
 

Answers and Replies

  • #2
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Why the current entering and leaving the battery in an elctirc circuit needs to be same??plz provide a mathematical proof for this.
thanks
Hi harshraj216 and welcome to Physics Forums!

Mathematical proofs are for mathematics. This is a physics/electronics question. Are you thinking of Kirchhoff's circuit laws? Please provide more info what you are thinking about.
 
  • #3
Integral
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Electrons do not "pool" any where, every electron that leaves the battery must return. Where else is there for it to go? Since current is electron flow, current out must equal current in.
 
  • #4
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It is not really impossible. Bring one pole of an isolated battery close to a charged vandegraafgenerator, while keeping the battery in your hand, and making sure your hand is earthed. When the spark occurs, a current pulse will be entering the first pole of the battery while there is no current leaving at the other pole.
This also applies if you connected the poles of the battery by a high resistance (a simple 'electrical circuit'). The resistance should be high compared to the impedance for the current pulse to your hand.
 
  • #5
sophiecentaur
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It is not really impossible. Bring one pole of an isolated battery close to a charged vandegraafgenerator, while keeping the battery in your hand, and making sure your hand is earthed. When the spark occurs, a current pulse will be entering the first pole of the battery while there is no current leaving at the other pole.
This also applies if you connected the poles of the battery by a high resistance (a simple 'electrical circuit'). The resistance should be high compared to the impedance for the current pulse to your hand.
Have you actually measured this lack of current, you claim? Are you including the self capacitance of the battery? Some charge will still flow to the unconnected terminal.
A good justification why current is maintained is that, when more charge flows onto an object than flows off it, the forces on the charges rapidly become very high. Just work out the Coulomb force that is needed to bring two Unit (1 Coulomb) charges (say on two spheres) to within a unit (1metre) distance of each other. See this reference It is not at all surprising that significant charges do not bunch up in odd locations, like one end of a battery.
Any object can acquire a small unbalanced charge, the PD needed to charge it is Q/C, where Q is the charge and C is the capacity in Farads. Bear in mind that, until the recent introduction of 1F supercapacitors, the maximum value of available capacitors was around0.001F, that the capacitance of an object as big as the earth is only about 700μF and that a Van der Graaff ball is about 20pF. No wonder it's hard to store much charge at all, if you are limited to reasonable values of voltage.
 

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