Nice and in depth! Can't we just simplify the concept down? (a) measure the open-circuit voltage. (b) load the cell with an appropriate resistance. (low enough to tease-out the predicted internal resistance) (c) calculate the loaded current (V/R) (d) calculate internal resistance. (Vunloaded-Vloaded/loaded current) Are we trying to eliminate some fringe effects that might make a single reading super inaccurate?
It's a good point and internal resistance can be determined with a single measurement; however, it is good to use a range of currents to check the internal resistance is a constant (at least, to check it doesn't depend on current and can be described as ohmic). The straight line indicates that. Of course there's another less satisfying reason for taking a range of measurements and plotting a graph: it's an opportunity to check that students can draw and analyse graphs correctly 🙄 we look for as many opportunities as we can.
@@PhysicswithKeith And we must be careful to minimize nasty errors from contact resistance and other gremlins. It would be easy to corrupt the measurement with sloppy practice. I always try to do a 4-terminal style measurement by probing the battery terminals separate from the contacts to the load resistor- it's hard to explain this to students though...
Nice and in depth! Can't we just simplify the concept down? (a) measure the open-circuit voltage. (b) load the cell with an appropriate resistance. (low enough to tease-out the predicted internal resistance) (c) calculate the loaded current (V/R) (d) calculate internal resistance. (Vunloaded-Vloaded/loaded current) Are we trying to eliminate some fringe effects that might make a single reading super inaccurate?
It's a good point and internal resistance can be determined with a single measurement; however, it is good to use a range of currents to check the internal resistance is a constant (at least, to check it doesn't depend on current and can be described as ohmic). The straight line indicates that.
Of course there's another less satisfying reason for taking a range of measurements and plotting a graph: it's an opportunity to check that students can draw and analyse graphs correctly 🙄 we look for as many opportunities as we can.
@@PhysicswithKeith And we must be careful to minimize nasty errors from contact resistance and other gremlins. It would be easy to corrupt the measurement with sloppy practice. I always try to do a 4-terminal style measurement by probing the battery terminals separate from the contacts to the load resistor- it's hard to explain this to students though...
The Panasonic D Cell RS pt No 860-2935 has quite a good datasheet.