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# Potential Divider Question Watch

1. Hi Guys

I've got a practical question paper I've been asked to do.

I've used a thermistor in conjunction with a variable resistor.

I've plotted resistance of the thermistor for 10 temperatures from about two degrees all the way to a hundred.

I've then been asked and successfully drawn a calibration curve for Resistance on the y and Temperature on the x. Well the next question is a little odd. no voltage readings at this point from the supply or variable resistor. while I have taken them separately from the required readings you can consider them unknowns.

The question asks exactly: "using your calibration curve and the potential divider equation V1 = (Vsupply x R1)/(R1+R2) determine values for the supply and resistance of the variable resistor.

I know how to apply a potential divider equation but not with three unknowns. There must be a way to utilise the resistance curve readings to obtain them but for the life of me I can't see it.

Any help would be greatly appreciated!
2. I've struggled a bit to work out exactly what it is you are trying to achieve.

If you have resistance vs temp of the thermistor and you want to utilise the whole curve then the curve midpoint will correspond to when V1 = 1/2 of Vsupply.

If I place R1(thermistor) on the bottom and R2(varaiable) on the top, find the midpoint on your curve, read off the resistance and then the value of the variable will be equal to this. I think the supply voltage can be any value, it depends on what voltage range of V1 you are looking for.

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Updated: December 16, 2010
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