Two batteries with inner resistor in parallel

  • #1

Homework Statement:

two batteries A and B are connected in parallel, and an 80 ohm resistor is connected across the battery terminals. the e.m.f and the internal resistance of battery A are 100V and 5ohms respectively, and the corresponding values for battery B are 95V and 3ohms respectively.

Relevant Equations:

Calculate the value and direction of the current in each battery.
I am kind of stuck at this exercise and I would like some help.

Thanks a lot!
 

Answers and Replies

  • #2
berkeman
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Homework Statement: two batteries A and B are connected in parallel, and an 80 ohm resistor is connected across the battery terminals. the e.m.f and the internal resistance of battery A are 100V and 5ohms respectively, and the corresponding values for battery B are 95V and 3ohms respectively.
Homework Equations: Calculate the value and direction of the current in each battery.

I am kind of stuck at this exercise and I would like some help.

Thanks a lot!
Please draw the circuit and show us how you would set up the KCL equations. Thanks
 
  • #3
Hi berkeman,

I started to calculate the terminal voltage, cause I thought that might help.
v= terminal voltage

(v/80) + (v-100)/5 + (v-95)/3 =0

v=94.66 V

with that, I calculated the current across the 80 ohm resistor:

I=v/R = 94.66/80 = 1.183

From the answer sheet, I know that this is correct as it is the sum of the individual currents in each battery.
But I do not know how to calculate it. I tried using the current divider rule, but it doesn't work.

Thanks for your help.
 

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  • #4
berkeman
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Ah, sorry, the drawing helps a lot. I thought the resistor was in parallel with the mismatched batteries, so that's why I asked for the KCL equation(s).

Since it is just one loop per the figure, a KVL equation is the better fit. Can you write that equation to see if it helps? The current around the loop through the various components is the same, right?
 
  • #5
phinds
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Homework Statement: two batteries A and B are connected in parallel
As has been pointed out, they are then NOT in parallel. This is not just semantics. It is important to use proper terminology in science.
 
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