Tricky V I Graph Need help please

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Homework Help Overview

The discussion revolves around interpreting a voltage-current (V-I) graph related to a battery and its internal resistance. Participants are exploring the implications of the graph's slope and the relationship between current, voltage, and resistance in the context of circuit analysis.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants are questioning the meaning of the gradient of the graph and whether it should be positive or negative based on the configuration of the voltmeter. There are discussions about the effects of varying load resistor values on current and voltage measurements, as well as the implications of measuring voltage across the battery versus the load resistor.

Discussion Status

Some participants have provided insights into the relationship between current and voltage, suggesting that the graph may exhibit a negative slope under certain conditions. There is ongoing exploration of how to accurately represent the graph and what measurements are necessary to determine the electromotive force (emf) and internal resistance.

Contextual Notes

Participants are grappling with the definitions and implications of measuring voltage at different points in the circuit, particularly concerning the internal resistance of the battery and the overall circuit behavior. There is a noted confusion regarding the measurements and the expected outcomes based on the circuit setup.

Steve12345
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What do you mean by 'gradient'?

You might consider taking more than 1 measurement of I and V ...
 
Last edited:
Steve12345 said:
need help with this question, is the gradient negative or positive since the voltmeter is over the battery?
Here is the image (sorry for making you tilt your heads)https://www.dropbox.com/sh/v6ydqbfrg20whtb/ZWR-r9ZOSH?lst#f:q17.JPG

As the load resistor value gets smaller, the loop current increases, and the measured source voltage decreases because of the increasing voltage drop across the voltage source's internal resistance.

Does that make sense? Can you now show us your work on the graph?
 
berkeman said:
As the load resistor value gets smaller, the loop current increases, and the measured source voltage decreases because of the increasing voltage drop across the voltage source's internal resistance.

Does that make sense? Can you now show us your work on the graph?

I drew a line that made a triangle from the V axis to the I axis, so when the current was at its highest V was 0 and when V was at its highest I was 0, so it was a negative slope.

I used emf= V+Ir and rearranged it go get emf - Ir = V. I am confused at wether the graph should be the a positive slope since the voltmeter is measuring the battery and not the load resistor if you get where I am coming from
 
berkeman said:
As the load resistor value gets smaller, the loop current increases, and the measured source voltage decreases because of the increasing voltage drop across the voltage source's internal resistance.

Does that make sense? Can you now show us your work on the graph?

So I am saying I drew it like this http://www.s-cool.co.uk/a-level/assets/learn_its/alevel/physics/Resistance/internal-resistance-emf-and-potential-difference/Finding%20the%20internal%20resistance.gif

Does it make a difference to the graph that were measuring V at a different point
 
Last edited by a moderator:
Steve12345 said:
So I am saying I drew it like this http://www.s-cool.co.uk/a-level/assets/learn_its/alevel/physics/Resistance/internal-resistance-emf-and-potential-difference/Finding%20the%20internal%20resistance.gif

Does it make a difference to the graph that were measuring V at a different point

Your graph is fine as far as it goes.

I don't understand your question abot V being measured "at a different point". The problem shows exactly where V is measured - across the battery including its internal resistance. Your equation V = emf - I*r fully corresponds to the diagram of the problem.

Now, how do you propose to construct your graph? You don't know emf or r. You're supposed to use the graph to determine emf and r.
 
Last edited by a moderator:

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