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The following exercise for a voltage divider is really easy to accomplish in the hardware setting with a fixed resistor, a resistance wire, a voltage source and a voltmeter. The process is designed to solidify the concept of a voltage divider. I'm having difficulty modifying it to be used with CircuitLab since the simulation doesn't allow for a parameter to drop from a given value to zero in a sweep.

I'm including a link to my Lab instructions for my usual "hardware" class so you understand the process I usually request of my students.

https://drive.google.com/file/d/1dWtSpjRIpEqBrFCAzUXKE4Fyvhf8lloG/view?usp=sharing

This is the circuit I've been playing with, but it doesn't match the Lab process that I want. Any ideas about matching simulation with hardware?

https://www.circuitlab.com/editor/#?id=bgyf64tvbcz2

Thanks as always, Carol Strong UAH

If I've understood the problem correctly, the schematic below "slider Divider" allows a DC Sweep to increase the value of R2.K (0 to 1, in steps of 0.01), thus decreasing the value of R2 in the circuit.

Note the orientation of R2 - I've put in explicit designations of "A" and "B", as you can't see these directly from the circuit.

https://www.circuitlab.com/circuit/rkzp8qdw5nsc/slider-divider/

Just an idea, maybe rather than using a potentiometer, use a resistor (you can change the label to show a variable resistor for clarity) and sweep its R value instead? this would reflect the questions in your shared doc that talks about the values of R1 and R2, rather than R1 and the product of R2's resistance and its position (R2.R*R2.K)...unless this is a calc you'd like your students to make as well?

I suppose you would still have an issue when R2.R=0, but this is a standard simulator behaviour (and maybe a good lesson about ideal components&simulations vs real life,RCL parasites etc), but you can start the decade sweep at say 1mOhm and end at 1MOhm play with points per decade etc ..

Also, potentiometer is a voltage divider in a box, arguably this circuit could be made with just the potentiometer and output going off the central tap. R1+R2 would be constant but their ratio would change... this to me paints the picture of a voltage divider. I'm just going off how I've been learning electronics and how I've been using CircuitLab to help me out with this.

I see what you all are going for with the potentiometer R2 and I headed this way. I don't understand the advantage of the "R2.K" parameter. I think once I have that hurdle jumped in my brain I'll be good.

So, would love a quick explanation of ".K" please. I've looked under the Documentation and I can't find references, though likely I've just missed it. I'm a bit panicked since today is the first day of online lectures and I have 495 students in my beginning class. The smaller class of Electronics should be easier, but learning the new simulator is a challenge for the small class. ;-)

Thanks for all your help, Carol Strong UAH

K is simply the tap fraction or wiper position between 0 (min) and 1 (max) R is the total resistance through the potentiometer (between pins 1&3 or A&C) R@Tap = Pot.R*Pot.K

Have a look at the DC sweep as set up. K value is swept betwen 0 and 1 (also note this doesnt throw a zero resistance error when K=0 unlike a resistor would if you'd sweep its R value).

Thanks @oskarhumnicki and @hevans:

Thanks so much, I think I understand the .K parameter better now. Thinking of it as a percentage between 0 and 1 helps. I'll look at your details. Is there a place I should have looked in your documentation to find this trick?

The other possibility of multiple tiny resistors, which I had considered, also might be good since this will only be their 2nd lab for the semester.

I may give them hints about doing the problem both ways to give them tools for later circuits.

Great ideas and I love the quick responses,

Carol Strong UAH

No worries, I'm not sure whether its in the documentation, but there is a tooltip in the dialog, when you hover over any parameter, there is a brief description on the bottom left. If you're referring to getting around the zero resistance error, this was just the case of experimenting, i wanted to sample voltage at the output of an amplifier but that needs to be connected to ground to simulate, but voltage at ground is 0 by definition, and so is the entire length of "wire" between the output and ground, placing a high value potentiometer and setting the tap to 0 and measuring from it was the easiest way i found to get a good reading... it was this or 2 resistors (output -> v small res -> v big res -> ground)

I definitely think @hevans' solution is a perfect application of how they would prove circuits in real life. The potentiometer gives a nice visual of the concept of potential difference fall across a resistor, especially given the symbol - oriented vertically it doesn't even need labels, this symbol and working principle then extends beautifully into what @hevans has prepared as a complete exercise, the ladder is the potentiometer track - the long resistor bit of the symbol, V2 is our tap. Before we had an option to move V2 by percentage of the overall resistance, now we are splitting this total resistance into discrete chunks and moving V2 only there, the principle is the same.

Hi @strongc. I believe the .K parameter EF82 is referring to in his answer is the sweep fraction of the potentiometer. It is definitely a good way to approach the problem if students are already familiar with the physical (real life) version of a pot. Looking at you exercise though, it seems that you mostly want to students to explore measuring voltages at different points along a resistive wire. In that case I would do something like this, and ask students to actually simulate the DC voltage at different points along a string of small resistors.

In my opinion this most closely matches what a student might do in a lab, and help build that intuition of what happens when you probe circuits at different points.

Thanks @oskarhumnicki and @hevans:

Thanks so much, I think I understand the .K parameter better now. Thinking of it as a percentage between 0 and 1 helps. I'll look at your details. Is there a place I should have looked in your documentation to find this trick?

The other possibility of multiple tiny resistors, which I had considered, also might be good since this will only be their 2nd lab for the semester.

I may give them hints about doing the problem both ways to give them tools for later circuits.

Great ideas and I love the quick responses,

Carol Strong UAH

Thanks to all of you for your ideas on the Resistance Wire Voltage Divider experiment for my Electronics students. I’ve decided to require BOTH options:

a. the series of small resistors to replace the R2 resistor and

b. one of the two potentiometer examples that you all gave me and that I finally found in the CircuitLab Textbook

The series suggested by @hevans is the closest to mimicking the Lab description without actually having a resistance wire. It will be easy for them to understand and to answer the prompted questions in the Lab.

The Potentiometer options give the students another way to solve the problem and it also gives them much needed insight into how to use the simulation version of a Potentiometer correctly within CircuitLab. You all taught me about the R.K style of sweep data and I’ve got all sorts of ideas about it now! Thanks to @EF82, @oskarhumnicki and @hevans .

You all have been very supportive with ideas that I never would have come up with. The semester learning experience will be much better because of your help.

Carol Strong UAH