Why Does the Internal Resistance Graph Have a Negative Gradient?

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SUMMARY

The internal resistance graph of a battery exhibits a negative gradient due to the relationship defined by the equation E = I(R + r), where R represents the total resistance and r denotes the internal resistance. This leads to the equation V = E - Ir, indicating that the voltage decreases as current increases, resulting in a negative slope when plotted. The key takeaway is that the gradient of the voltage/current graph is equal to -r, confirming that internal resistance affects the overall circuit behavior.

PREREQUISITES
  • Understanding of Ohm's Law and its application in electrical circuits.
  • Familiarity with the concepts of voltage, current, and resistance.
  • Knowledge of graphing linear equations, particularly the slope-intercept form.
  • Basic principles of internal resistance in batteries and cells.
NEXT STEPS
  • Study the implications of internal resistance on battery performance and efficiency.
  • Learn about the characteristics of ohmic vs. non-ohmic resistors.
  • Explore the use of the equation E = I(R + r) in practical circuit analysis.
  • Investigate methods to minimize internal resistance in battery design.
USEFUL FOR

Electrical engineers, physics students, and anyone involved in battery technology or circuit design will benefit from this discussion.

Vaseline
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When taking internal resistance into account, voltage/current graph has negative gradient (i.e. internal resistance).?

My thoughts...

Because for ohmic resistors, graph has a positive gradient. Why does one say that when V=0, Current = max, whilst the other says that when V=0, Current = 0?
 
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Vaseline said:
When taking internal resistance into account, voltage/current graph has negative gradient (i.e. internal resistance).?

My thoughts...

Because for ohmic resistors, graph has a positive gradient. Why does one say that when V=0, Current = max, whilst the other says that when V=0, Current = 0?

My question was answered in that thread, this is the result I got.

E = I(R+r) where R is the total resistance in the circuit and r is the internal resistance of the cell or battery. From this we can see that,

E = V + Ir

and,

V = E - Ir

When plotting a graph of potential different against current it is clear that the current I has a negative co-efficient: -r. Hence -r is the gradient of the line, and E is the y intercept. y=mx +c (remember?) this is just V=-rI+E.
 

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