About OHM and his LAW

OHM's LAW - What it is. How it works.
A personal LEARNING AID for the interested and patient learner. Just read the following pages with care or call them up using the HELP function under program execution.
A) Learn the color code for resistors through practice.
B) Learn to calculate rsistance for SERIES, PARALLEL, SERIES-PARALLEL circuits. Circuits are auto-generated and displayed. Answers are verified and a score card is kept. Chose a level of difficulty: (E)asy, (D)ifficult, (E)xpert. A calculator and notepad is needed for the more advanced levels. Just a notepad will do for the (E)asy level.

IMPORTANT: Answering questions on impulse will lead to failure and frustration. READ the instructions that preceed the cursor with care and respond in kind before going on (pressing ENTER).

REMEMBER: GIGO - Garbage In, Garbage Out

Step 1 A summary of what is available

HELP : Start by reading ALL the pages (5) in the (H)elp section. The pages are presented below along with some expanatory note.

Comments

[AKA1]

I've always known OHMs law and Rs in series and parallel BUT did NOT know (or forgot) how to calculate Networked Rs - so spending 10mins on STEP 5 was very satisfying especially as working from the RHS calculating series R taken in parallel with next R loop to the left and so on NOW seems very LOGICAL - A much appreciated intuitive tutorial! NOT wishing to be critical BUT why make life hard and write R.exe as a CONSOLE app rather than a Windows based program? Your successful project was my reason for registering with Instructables.com SO thanx AKA1 - so thanx

[LasVegas]

When I took Basic Electronics in 9th grade, this was a quiz the teacher put on the board the first day. He offered an extra A grade to anyone that produced the right equation that solved it...

[richjd]

I remember the same problem given by one of my teachers. Needless to say I did not get an 'A'. From what I remember, the solution is as follows:

[shredder03]

thats a solution from point A to the furthest point B. If the points were on the same face, so that one resistor is in series with A, what would the resistance bee then? What about to the opposite side of one face, on your cube in the problem it would be the corner where you have written Vs

Currents cannot be used because they do not follow a symetrical pathway, from A to the closest point *im calling this B* you would have 3 possible pathways, and from A to the opposite corner of a face *I am calling this C* you would have 2 possible pathways.

[richjd]

Here is a blowup of the summary.
Point B is a point from where measurements must be made and it is NOT a three resister array point.
From B Rvr and Rvg are in parallel and the resistance for BRANCH B (RatB)=1/2(Rvg)=1/2(1/3R)=1/6R=R/6
RatB, Rvq and Rvs form a series BRANCH and:
Rt=RatB+Rvq+Rvs=(R/6)+(R/3)+(R/3)= (5/6)R
Therefore Rt=5/6 Meg ohms.

[richjd]

Here we go again! Been retired too long! Here is a more detailed explanation of the 12 Resistors Cube.

For simplification the VERTICIES of the cube are color coded and involve all 12 resistors: Bu(blue), Rd(red),Bl(black), Gn(green). 'R' is used as R=1 Meg ohms throughtout. See the diagrams ::: NOTE that the POINT B is NOT one of the verticies with an array of resistors. It is the point from which we make our final measurement.

For any vertex, say Bu, there are three equal resistors in parallel and their combined resistance is: 1/Rbu=(1/R1)+(1/R2)+(1/R3)=(1/1)+(1/1)+(1/1)=3
and Rbu=R/3 (one-third one of the resistors)
Since all the vertices are the same, we conclude:
Rbu=Rgn=Rrd=Rbl=R/3

:::In the diagram showing equivalent resistors ::: We want to measure from POINT B::: We note that we can connect; RED to B, BLACK to B, GREEN to B, but there is no path to connect BLUE to B except through one or more colors. We conclude the EQUIVALENT circuit shown::: A SERIES/PARALLEL CIRCUIT between POINTS A and B, and........
we calculate the BRANCH resistance in the parallel branch (R at B, RatB) as follows: RatB=(Red)(Green)/(Red+Green)::: RatB=(R/3)(R/3)/(R/3+R/3) or simply RatB=(1/3)(1/3)/(1/3+1/3)= (1/9)/(2/3)=1/6 or R/6.

::: We now have BRANCH circuit consisting of RatB,BLUE,and BLACK in series and Rt=RatB+RBlue+RBlack. Simply put
Rt=(R/6)+(R/3)+(R/3)=5/6R= 5/6 Meg ohms, the resistance between POINTS A and B on the Resistors Cube.

[cpotoso]

(removed by author or community request)

[LasVegas]

Except for your typo… It's 1/3 + 1/6 + 1/3 = 5/6V, therefore 5/6MΩ or 833.33KΩ :)

[richjd]

Find out more about the RISISTORS CUBE problem. Visit

http://www.radioelectronicschool.net/files/downloads/resistor_cube_problem.pdf

http://www.physics.upenn.edu/courses/gladney/phys151/bonus1_solution.html

richjd

[richjd]

Dear Las Vegas:
You did'nt say if you got an 'A' for solving the RISISTORS CUBE PROBLEM when in the 9th grade.
I have presented my solution with supporting comments; Rt=(5/6)Meg ohms. I am interested in knowing of other approaches to a solution and would like to know yours. Would you share it with me? If you decline I will not be offended.
Some time ago I was given the 'solution' of a respected collegue as Rt=(1/4)(1/3R)=1/12 Meg ohms. You can guess how he arrived at that conclusion. Most people just give a number as a solution. I am more interested in the logic (method) used to arrive at a solution. Hope to hear from you.
Sincerely, richjd.

[LasVegas]

My solution followed the same logic as cpotoso's. Labeling the other corners A1, A2, A3, B1, B2 & B3. Then following the current and applying Ohm's Law to determine the total resistance. Yes, I among others, did receive the credit. I did not solve it though until learning Ohm's Law later in the course. I have to admit that I do like your logic for the solution as well. I wouldn't have approached it from that direction. Also, thanks for the links. I've never seen that problem elsewhere on the net. Your collegue's solution was flawed to begin with and I suspect wasn't thought through long.

[cpotoso]

(removed by author or community request)

[mikesty]

250 kOhms???

[LasVegas]

Some guessed correctly and incorrectly. Others actually built the bridge and measured it! Of course, none in either group got an 'A' out of it.

[Tool Using Animal]

Half a meg

[LasVegas]

Again; Without an equation, there would be no credit wether your answer were right or wrong… Perhaps more conventional 2 dimensional schematics of the circuit would help:

[Tool Using Animal]

I'm to buzzed for equations lets say it's six three meg resistors in parallel so 3 meg divided by number of legs equals half a meg.

[shredder03]

I have a question for you. What if you're trying to find the resistance from the starting point to the point closest to it? If you could get back to me ASAP, it would be greatly appreciated.

[supes]

From what I am told from my OLD electronics teacher...They used to use "Bad Boys Rape Our Young Girls, But Violet Gives Willingly (for SILVER and GOLD!)" when he was growing up but that slowly phased out due to its offensiveness. I dont think many people have a replacement for it, thus a device like this is not used.

[theRIAA]

awsome

[dan]

this looks very useful for classroom use, are you teaching a class with it currently?

[richjd]

Hi dan: I wrote the program in 1989 when I was teaching Basic Electricity and Digital Electronics courses. I retire in 1992 and took several teaching aid programs which I had written in the 80s out of moth balls. I made extensive use of this program and I guess it is still pertinent today. Glad you liked it. Sincerely, Richard

[jaredforshey]

I found this one penciled into a Navy issue electronics textbook from around 1940: "Bad Boys Rape Our Young Girls, But Violet Gives Willingly (for SILVER and GOLD!)

[Shark500]

my father (an electritian @ the budwizer brewary in newark nj) tough my that. i never forgot that.

[LasVegas]

My father taught me a more politically correct version when I was too young for that version that went: "Big Boys Race Our Young Girls But Violet Generally Wins Good & Straight!" Same results, less offending!

[westfw]

Thanks for adding the screen shots!

[westfw]

Somewhat more politically correct: Bad Booze Rots Our Young Guts, But Vodka Goes Well I found it easy enough to memorize based on the roy g biv sort of spectrum, what with brown and black being "below" red and white being "above" violet. Two things memorized at once!

[Elastometer]

At school we used to remember the basic colour code system by means of the following: 'Big Bastards Ravish Our Young Girls But Virgins Go Without' For this reason - I'll never forget the code! Excellent Instructable though and very educational for those getting started in Electronics.