# Potentiometers and rheostats

What's the difference between incoporating a rheostat and a potentiometer into a simple circuit?

When you decrease the wiper resistance on a potentiometer, the voltage drop between the potentiometer resistance and load resistance changes so that there's a greater voltage at the load.

Well, when you decrease the wiper resistance in a rheostat, the voltage drop ratio between the rheostat and the load changes as well.

So when you decrease the wiper resistance on either the rheostat or a potentiometer, you allow greater voltage to the load.

When you decrease the wiper resistance on either device, you are also allowing more current to flow to the load.

So with both devices, adjusting the wiper arm adjusts both voltage and current to the source.

The only difference I can see between the two devices is that a rheostat will provide a single path of current from the voltage source through the load while a potentiometer will provide an alternate/additional path for current, some current through the load and some bypassing the load through the parallel arrangement.

Either way, adjusting the wiper of either device will adjust voltage and current (thus power) at the load. So why would one device be preferred over the other in various circuits?

What is the purpose of having the extra path of current in a potentiometer?

What can a potentiometer do that a rheostat can't?

Thanks, I'll ponder that for a while and come back with any further questions of they arise. Thank you

sophiecentaur
Gold Member
What's the difference between incoporating a rheostat and a potentiometer into a simple circuit?

When you decrease the wiper resistance on a potentiometer, the voltage drop between the potentiometer resistance and load resistance changes so that there's a greater voltage at the load.
It all depends what you want to achieve. It is an 'Engineering Choice" that needs to be made each time.
A Potential Divider Circuit is always passing some current, which may not be handy for a battery operated device. A rheostat only passes the load current.
A Potential Divider can give you a range of voltages out from Zero to the Maximum but a Rheostat will only introduce a certain maximum of series resistance to limit the current supplied to the load.
A rheostat needs to have a large maximum value of resistance (perhaps many times the resistance of the load) if you want to be able to reduce the output current to a low value. That means it may need many turns of thin wire which, when you want to supply a lot of current to the load, the 'top' few turns of resistance wire will be passing a high current through a short length of very thin wire and it may burn out those few turns. Otoh, a potential divider can use fatter wire to pass a high maximum current and yet still give you Zero volts.
Plus various other differences.

The wiper resistance is only relevant when it is comparable with the resistance of the load. It will not affect the output volts from a potential divider if the load is a high resistance.

• Ocata
berkeman
Mentor
Nice link to answer the OP's question directly. Thanks @Bystander And here's an updated version of the Bourns Trimmer Primer that has been a classic for many years. Nice of them to update it:

https://www.bourns.com/pdfs/OnlinePotentiometerHandbook.pdf

• Ocata, Bystander and Tom.G
Bystander
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