Wednesday, January 6, 2010

Chapter 1 - Exercise 1

Okay, if you have the book, you already know what Exercise 1 is all about - licking a battery.

Did it hurt? Nope... tingled... more of a surprise than anything...

After drying my tongue, I had to try a few times to feel anything. But even then, it wasn't much and may have been my imagination.

But the author's point is well taken - our bodies can conduct electricity, even from relatively weak sources like an alkaline battery.

Part of Exercise 1 is all about using your multimeter to take some measurements... unfortunately, my cheapy meter doesn't have the best of settings and can't go as high (with both ohms and voltage) as my autoranging one. I followed the instructions in the book (no less than 100k resistance) and took a measurement of my tongue... no luck. I had to crank up my meter to 2000k before I could get a reading. Maybe it's my meter, but the 200k setting didn't even provide results. (Maybe my tongue is super resistant!)

At 2000k setting, it finally started giving me results... they didn't match the target estimate in the book, but that's okay - I understand what the author is trying to get me to understand... by drying my tongue (or moving the probes further apart), I'm getting a higher resistance reading.

Next, I ran a wet towel down my arm (okay, I licked my left arm the first time - don't judge me. But on the next two tries I figured a towel would give more consistent readings on my right arm.)

Here's what I got:

at 4" apart, the probes had a reading of .7 mOhms
at 2" apart, they gave a reading of .5 mOhms
at .25" apart, the reading was around .4mOhms

On dry skin, I couldn't get any reading... zero. Even after putting the probes about 1/4" apart.

So, what should you take from the reading and exercises for Experiment 1?

* First off... read the manual for your multimeter. It may seem obvious, but it won't hurt for you to read it and know what each setting is for...

* Make sure you understand the chart (page 6) covering Ohms... and how to convert these values in your head using the k (kilo) and m (mega)...

* Know the terminology for items with high resistance and low resistance...

* Know the resistance of your tongue... it will be on a test someday...

* Write a 3 page report on the man who discovered resistance (to be graded by Mr. Platt)...

* And do the last experiment (bottom of page 8) so you'll understand why it's a very bad idea to swim in the ocean during a lightning storm.

Finally, to close out this post, please take note of my lab book in one of the photos. I highly suggest you find something to write down your notes, results, etc. A book like this will help you keep track of your experiments, any variations you may try (and their results), supplies you've run out of, new supplies for future experiments, and more.

See you tomorrow for Experiments 2 and 3.


  1. I used filtered water instead of Distilled water, don't have a distiller at home :-), and was surprised at the difference between tap and filtered (even with an old filter).

  2. I have a question. I'm totally new to all this, just got my book in today. When I do the test with water, or on my tongue, the longer I hold the wires there the higher the resistance goes up so have no idea where it's at. The readings are all over the place so I don't get anything close to a consistent number. Also, I don't see much difference between a dry tongue vs. wet tongue.. or filtered water vs. salt water. Could there be a problem with my multimeter or did you have any trouble like this?

  3. Hi, RG.

    I, too, had problems getting accurate measurements with the tongue tests... but with the regular water vs salt water, it was very easy to distinguish the values. I'd suggest adding more salt to the saltwater... I mixed quite a bit in there.

  4. RG, my son and I had trouble, too, getting good readings on tongues and arms. The reading would start out low, climb and climb, and then vary wildly once it seemed to finish the climb. Also, it wasn't in the range the author described. Like you, this made me question whether my multimeter was broken and if I'd ever be able to take a good ohm reading.

    However, because I'm waiting on my component kit to arrive, I dug out some old printed circuits (a modem card, etc.) and began measuring the resistance of components soldered onto the board. Sometimes I'd need to adjust the meter's range to 'find' the resistance, but in all cases, I was able to get a really solid reading (i.e., it'd get to 8.0 ohms and just stay there, or maybe shift slightly between 8.0 and 8.1).

    I did learn that the meter seems to start out low and climb until it hits a solid reading, and that this can take a few seconds to stabilize on the ultimate reading. If the range is set too low, it'll sometimes quickly give a low reading and climb until it exceeds the range, at which point it gives an error. Simply move to the next higher range and try again until it stabilizes.

    My worry is that as a first exercise, tackling something that gives such a wildly inconsistent reading can throw newbies (like me) off track. Something to consider if there's a second edition.

    Also, on the 'battery to tongue' exercise, we found you could more easily feel the difference if you dry your tongue, apply the battery, remove the battery, pull your tongue into your mouth and wet it, and then apply the battery again. Because the zaps are just a couple seconds apart, you'll much more acutely notice the increased power of the second (wet-tongue) zap.

  5. Well I guess I am coming a little late to the party :).

    While this experiment was pretty straight forward I did find it interesting the difference in resistance between my tap water and bottled water (55Kohms vs 175Kohms). I guess that's well water for you. I also thought it would be interesting to check the resistance of each glass of water (120ml) after I added a 1/4 teaspoon of salt. I found that the resistance was essentially equal at about 25Kohms. After a little math I discovered that a 1/4 teaspoon of salt in a 120ml glass of water dwarfed the disolved salt quantity in my tap water by a factor of about 20:1. It's always nice to be able to put things in perspective.

    By the way, as soon as my wife heard that the first experiment involved touching a 9v battery to your tongue she said: "That's definitely a boys book!" :)

  6. I had to crank my brand new BK Precision 388B (Mr. Platt's favorite) up to 4 M before getting a reading of 3.8 M for my wet tongue...