Homework Help: Use of potentiometer or rheostat to determine resistance – need clarification

1. Jun 11, 2009

elvinc

Hello

I understand

1. The problem statement, all variables and given/known data

1) a potentiometer can be used to divide a voltage to any value between zero and the voltage source. This can be used to place a variable voltage through a resistor

2) A rheostat (variable resistor) which is placed in series with the resistance to be measured can create a variable current through the resistor.

Now if voltage and current is measured in both setups as either the potentiometer or rheostat is changed both will generate pairs of values for voltage across and current through the resistor under test.

2. Relevant equations
V/I = R

3. The attempt at a solution
Plotting V against I for both sets of experiments would enable me to calculate the resistance as gradient of the plot. So which method (if one is to be preferred) should be used to determine the test resistance? Why?

Thanks,

Clive
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jun 11, 2009

LowlyPion

Welcome to PF.

Intuitively I would choose the potentiometer, because I could expect to want to control the voltage source across the test piece. A rheostat may have some thermal variance with different current loads (I2R), that I would expect a potentiometer would mitigate to some degree.

But in large part it depends on the size of the resistors you would be trying to measure. If they are very small values of ohms, things could be more challenging regardless of what method you would choose.

That's just me. Others may have better reasons than my intuition to choose one or the other, and if so, then by all means help the fellow out. It hasn't been addressed for half a day.