EMF's in series how does this work ?

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Discussion Overview

The discussion revolves around the behavior of electromotive forces (e.m.f.) in series circuits, specifically involving a secondary cell and a primary cell with different e.m.f.s and internal resistances. Participants explore the implications of these differences on current flow and terminal voltage, referencing a specific homework problem.

Discussion Character

  • Homework-related
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions how two cells in series can have different currents, indicating a potential misunderstanding of the underlying concepts.
  • Another participant suggests that the current will vary based on which cell's voltage is being measured, implying that the measurement context affects the readings.
  • Several participants express confusion about the connection of the voltmeter and its impact on the measurements, with one explicitly asking for a diagram to clarify the setup.
  • A different perspective is offered, proposing to visualize the scenario as three objects in parallel (the two cells and the voltmeter), which may help in understanding the current distribution.
  • Participants note the significance of including internal resistances when analyzing the circuit behavior.

Areas of Agreement / Disagreement

There is no consensus on the interpretation of the circuit behavior, as participants express differing views on how to approach the problem and the implications of the voltmeter's resistance.

Contextual Notes

Participants highlight limitations in understanding due to the absence of a visual representation of the circuit, which may affect their ability to conceptualize the problem accurately.

hilly
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Homework Statement



A secondary cell having an e.m.f. of 2V and an internal resistance of 1ohm is connected in series with a primary cell having an e.m.f. of 1.5V and an internal resistance of 100ohm the negative terminals of each cell is connected to the positive terminal of the other cell. A voltmeter having a resistance of 50ohm is connected to measure the terminal voltage of the cells. Calculate the voltmeter reading and the current in each cell.

Ans given by book:72.8mA, 34.3mA, 1.93V

Homework Equations


Kirchoff voltage law.


The Attempt at a Solution



I can not understand how 2 cells in series can have a different current ? What concept am I missing ?
 
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The current will change according to which cell voltage you are measuring.

The voltmeter has a resistance of 50R... (that's some "voltmeter"...)
 
Is there a picture for the question? I'm not sure how the voltmeter is connected to measure the terminal voltage.
 
Defennder said:
Is there a picture for the question? I'm not sure how the voltmeter is connected to measure the terminal voltage.
Sorry no picture because the textbook has no picture only the words
 
zeitghost said:
The current will change according to which cell voltage you are measuring.

The voltmeter has a resistance of 50R... (that's some "voltmeter"...)
The book answer gives one voltage and 2 currents.
 
Instead of thinking about 2 batteries in series, try picturing the situation as 3 objects all in parallel (the 2 cells and the 50-ohm resistor).

Don't forget to include the internal resistances as part of the cells.
 

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