When starting an introduction course on electronics one of the very first things you need to do is to teach the very important concepts of ** Voltage**,

**and**

*Current***. They need to become intuitive, and an analogy that is often used is that with a flow of water, coming down from a reservoire.**

*Resistance*Well, I've found that it doesn't always work! **Many young students lack that feeling for physical fenomena, so I decided to show it experimentally.**

I made this experiment in an after school course about basic electronics, for curious groups of students ranging from 15 to 18 years old. Even if some of the older ones already had this *knowledge*, doing this personally improved their *understanding*, which is what's really important when studying scince, otherwise it becomes just a bunch of formulas.

The experiment itself is easy, with a lot of room for error and the results are pretty nice. Also, I've found that seeing the fenomenon helps the students visualize later on.

**PS: There's the Python script used to plot the data! Download from the step Analyzing your Data**

## Step 1: Build the Apparatus

The setup is very simple, you just need to hang one of the tanks somewhere and place the other tank below. In order to seal the point in which the tube enters the tank I used some epoxy. Also, **making a couple of lines on the top tank** *(as visible in the photos)* ensures that the amount of water trasferred is alway the same.

**A possible variation is to constantly measure the mass**, either by hanging the top tank from a scale or placing the second tank on a scale, and correlate the time to the mass transferred in that specific iteration. This should work fine, but notice that it **introduces a non-constant error**, since the average height of the water might not always be at the same distance from the point from which you measure the height.

Once everything is set up, you can **add some coloring to the water**, just to make it clearly visible. Food coloring works fine.

Remember to **close the valve before filling!**

I personally believe (and have believed since I was a student learning Ohm's law for the first time) that that the analogy (used since time immemorial) of a water tank (the voltage) pushing water (the electrical current) through a resistance (the pipe/tube) virtually useless! For one simple reason! Once the water reaches it's final container the pressure (Voltage) dissipates.

The true key to getting students/learners to understand Ohm's law (first time, every time) is to show them how a "closed/pressurised" hydraulic system works first!

I, as yet, have not found a single student who didn't understand the principles of pressure (Voltage), Flow rate (Current) and the relationship of two with respect to the diameter of the hydraulic pipes (Resistance).

Better still, using small hobbyist/experimental kits, small and easily alteraterable hydraulic circuits can be built and tested. Thereby making it easy for the student to investigate the difference between series/parallel hydraulic systems and to then be able to fully understand exactly how Ohm's law works!

Indeed, whenever I have used this method of teaching Ohm's law to teach a group of students I have never then heard a student talk about "Voltage through a component". The sure fire giveaway that the learner hasn't fully grasped the concept.

I would have thought that there were miniature style hydraulic kits for children just as there are electronics and chemistry lab/learning kits for kids.

Maybe a gap in the market there!

But do not give up, there i a chance... Proportional relation between pressure drop (height) and flow rate works at LAMINAR flow conditions at low velocities and small tube diameter (so it is contraproductive to try bigger one!). Briefly: if simple shear friction is the source of pressure drop, linear relation prevails, if the energy is consumed to create eddies/turbulences, the relation is quadratic.

There is much more to study, please use Google to search laminar vs. turbulent flow condition, critical Reynolds number, and pressure drop calculation. In fact, there IS a "law" describing linear pressure drop/flow rate relation - but it has very limited use for conditions I mentined and you should work at - see Hagen-Poiseuille equation.

According to Ohm's law, current must increase to infinity if resistance approaches zero. That is not the case if you pluck off the hose from the bottle (and still there is "voltage" - water level in the bottle), the flow rate will stay quite low compared to "infinity". This is due to the fact that for fluid flow, there is not only energy dissipation, but also energy conversion - pressure at the bottom of the bottle is converted into velocity according to Torricelli equation, which is a special case of Bernoulli equation.

In my opinion, it is important to make experiments attractive, but without sacrificing scientific correctness. Using similarity is OK, but without ironing unwanted data - this is the difference between "just-a-show" and "true science" (no matter how simple the experiment is), or mnemotechnics and understanding. So it is important to comment/admit the limitations of the results - keep in mind that in physics, "electricity" will be followed by "hydrodynamics" after couple of semesters :-)

Watt's Law describes the relationship, between Power and any two of the variables above. "Power is as easy as Pie." P= I * E, I squared * R, or E squared / R.

http://lcamtuf.coredump.cx/electronics/

The bottom bottle is filling as the top bottom empties - this is the equivalent of raising the ground voltage, thus reducing the potential difference of V as time progresses.

To confirm this simply remove the bottom bottle and let the water flow straight onto the ground, do this while re-timing and you should see a difference.

Very EXCELLENT Instructable!!!!

F=ma. Except when it is not.

E=mc^2. Except when it is not.

But the concepts are close enough for most cases. And more importantly, give most people a solid understanding of the universe that, otherwise, seems like magic.

"Except when it's not" is what makes more advanced topics interesting to those that want to learn more.

1) Altitude is a factor. Atmospheric pressure is non linear for height. It isn't much. You could have been measuring an approaching weather front.

2) Another consideration is that in order to maintain a constant potential difference between the two liquid levels, both containers must be the same diameter and be a constant diameter from top to bottom. If the containers are of a different diameters, the difference in height will vary with time and will affect the flow rate, which will introduce errors.

3) There is also the turbulence of the liquid in the tube due to bends, the straighter or more constant the better. Using a long very small diameter tube was smart.

Your results were very good. Great Job! Better than the average college science lab.