Use of potentiometer or rheostat to determine resistance – need clarification

[elvinc]

Hello

I understand

Homework Statement

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.

Homework Equations

V/I = R

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

 

[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.

 

[nlightner]

Hello Clive,

Thank you for your question. Both a potentiometer and a rheostat can be used to determine resistance, but the method you choose may depend on the specific setup and equipment you have available.

A potentiometer is typically used to measure an unknown resistance by comparing it to a known resistance. It allows for a precise adjustment of the voltage across the resistor under test, which can then be used to calculate the resistance using Ohm's law. This method is useful for measuring small or precise resistances.

On the other hand, a rheostat is more commonly used to vary the current through a circuit. By adjusting the resistance of the rheostat, the current through the circuit can be changed, and this can be used to calculate the resistance of the resistor under test. This method may be more suitable for larger resistances or when the voltage source is fixed.

Ultimately, both methods can be used to determine resistance, but the choice may depend on the specific setup and the desired precision of the measurement. I hope this helps clarify the use of potentiometers and rheostats in determining resistance. Let me know if you have any further questions.

Best,