# Internal Resistance Graph

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?

## Answers and Replies

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.