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Hi,

I am looking at purchasing some kind of variable resistor set up/rheostat/potentiometer for senior physics. We have a slide type one which is ancient. Can anyone recommend what to buy especially as I am a bit confused with the catalogues, they seem to cover different resistances, and there are different types. Is a rheostat and potentiometer much the same think? Is there one out there that has a dial rather than the old slide type. Any help would be most appreciated.

Thanks
Pilar

A potentiometer is a barrel type controller of voltage like a volume control on a home stereo. A rheostat as you said is a long cylinder shape with the slide control across the top that adjusts the voltage. Same outcome just different ways on controlling the desired output. Dick Smith has loads of potentiometers of every size where most Scienceware stockists will have rheostats! Below is the former without it's knob.

A teacher has asked me for variable resistors for a year 8 class on circuits. We have slide rheostats, resistor sets (with 7 different resistors in them) and potentiometers. All seem to work within a simple battery bulb circuit but only at one end of the range and go from on to off very quickly. The potentiometers seem to be the closest to what he wanted as they have a dial. I don’t have enough of any of them for a full class as we usually only use them for senior physics which are much smaller classes, so I will need to buy more. The potentiometers are only a few dollars from Jaycar so seems like the best bet. If I want them to work over a bigger range what would be the best type to buy? I currently have B10K. Should I go down to 5K?
Thanks

The slide rheostats we have around 11 ohms . If connected to a 5watt bulb there will be some slight dimming from one end to the other .
If we use them on 35 watt bulbs , they go from full on and dim over the full length of the slider ....they are a good match for this type of demo .

A 10k Pot will as you say only work right at one end where the resistance is very low . 5k will be no better . 10K =10,000ohms.....a far cry from 11 ohms

Something closer to 47ohms would be a good value for dimming a 5 watt globe but you will need one rated at about 5watts otherwise it will smoke up pretty quickly.

Edit : if your slide rheostat is only working at one end , it may need a restoration viewtopic.php?f=42&t=4897

They go as low as 500 ohms so should I get those then? The lower the better?

Does it look like this ?
I know it says 1K but its the pic Jaycar had for it . At 500 ohms you will probably find that you get all the action in the first 10% of the pot and its dark for the remaining 90% of rotation if you are using a 5watt lamp . Also these pots are rated at less than 0.5watts so it will burn up while the lamp is glowing .

You could use an LED with a higher value pot but then you need to add a series limiting resistor and even than you can guarantee the kids will hook the LED straight to the power supply and blow them in microsecond ...so still not a solution .


Haines have got 50ohm wirewound 3Watt potentiometer for about $35 that would be just the ticket for adjusting a 5 watt lamp .
That's what I'd be getting if I had to replace the ones we have .
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Yes, that’s what I have and was going to get more of. Sounds like not the way to go then. Thanks for that, I’ll have a look at Haines.