You are invited to Log in or Register a free Frihost Account!

# Internal resistence change

chatrack
In potentiometer experiment in our lab, internal resistence of a cell (leclanche cell) incresses with external resistance! Which is against theory, can give an explanation?
PatTheGreat42
There is a distinct possibility that either the experiment just messed up somehow, or that the potentiometer you used affected the resistance in a way you did not account for.
chatrack
 PatTheGreat42 wrote: There is a distinct possibility that either the experiment just messed up somehow, or that the potentiometer you used affected the resistance in a way you did not account for.

I doubt, whether maximum power transfer theroem can give some explanation, to the potentiometer method of measuting internal resistance.
Klaw 2
I doubt anyone can say what is wrong, can't you post the results pictures etc.
Dennise
I know nothing about leclanche cells but could this explain what you ares seeing?

Negative resistance is a property of some electric circuits where an increase in the current entering a port, results in a decreased voltage across the same port. This is in contrast to a simple ohmic resistor, which exhibits an increase in voltage under the same conditions. True negative resistors are theoretical and do not exist as a discrete component. However, some types of diodes (e.g., tunnel diodes) can be built that exhibit differential negative resistance in some part of their operating range. Similarly, some chalcogenide glasses[1] and conductive polymers exhibit a similar region of negative resistance as a bulk property.
Dennise
 chatrack wrote: In potentiometer experiment in our lab, internal resistence of a cell (leclanche cell) incresses with external resistance! Which is against theory, can give an explanation?

As you load the cell it discharges, which increases it's internal resistance.

Are you using a partially discharged or completely discharged cell in your experiment? To measure internal resistance, you need to draw enough current to see an external voltage drop. If you do this continuously for too long, you will discharge the cell.
chatrack
I think this is the possible correct answer