# OHM's Law Quiz

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#### T.Jackson

Joined Nov 22, 2011
328
:: OHM's Law Quiz ::

You any good with OHM's law?,then here's a quiz for you ...

Requirements:

• 6 resistors ...
• 5 specific Vrefs of: 1, 2.2, 3, 3.3, and 4.5VDC
• IT = 20mA
• Calculate value of R1 - R6
Rich (BB code):
              4.5V      3.3V      3V        2.2V      1V
|         |         |         |         |
5V o--/\/\/--+--/\/\/--+--/\/\/--+--/\/\/--+--/\/\/--+--/\/\/--o GND
R1        R2        R3        R4        R5        R6
Show all workings, natural voltages measurable from ground.

Last edited:

Joined Dec 26, 2010
2,148
This should be in the homework section.

The OP should not in any case expect to be given a worked answer to this problem.

#### T.Jackson

Joined Nov 22, 2011
328
It helps a lot to compose your text in Notepad with a fixed font such as Courier New; as otherwise it's more difficult to make sure things are going to line up.
Thanks for that.

#### T.Jackson

Joined Nov 22, 2011
328
This should be in the homework section.

The OP should not in any case expect to be given a worked answer to this problem.
LOL this is a test to see everyone's general knowledge. This is trade level Ohm's law which I passed years ago.

#### T.Jackson

Joined Nov 22, 2011
328
@SGT

Do you feel that this is a good alround test? I feel that if they can answer this, then they sort of know what they're doing.

#### SgtWookie

Joined Jul 17, 2007
22,210
It's an OK mini-pop-quiz. It would be more challenging if it had series-parallel circuits to solve.

#### T.Jackson

Joined Nov 22, 2011
328
You ever used a PC program called DC challenge?

#### T.Jackson

Joined Nov 22, 2011
328
That got very, very hard. I beat the thing in the end though.

Thing is, in mind it makes no sense that we are all talking about transistors and OP AMPs when we haven't a clue about ohm's law, which forms the entire basis for electronics.

#### SgtWookie

Joined Jul 17, 2007
22,210
No, I've never heard of a program called "DC Challenge".

I was formally introduced to Ohm's Law about, oh, 37 or so years ago, but I'd been using it well before then.

There are a number of E-books available by clicking the links at the top of every page on the site; that's where much of the basics are covered.

If you want a bit more in-depth, you could go through the Navy NEETS training series; downloadable for free in .pdf format here:
http://www.phy.davidson.edu/instrumentation/NEETS.htm
I went through a predecessor of NEETS back in the 70's.

I more often than not run through the math behind a circuit if I'm helping someone - just so they'll see how I arrived at the values that I did.

#### T.Jackson

Joined Nov 22, 2011
328
Do me a favour and solve that quiz? You seem faster than me.

There are a few ways to do it, but simply v / i won't cut it as two people have suggested.

I should have given the hint of RT

#### MMcLaren

Joined Feb 14, 2010
842
... but simply v / i won't cut it as two people have suggested ...
Why not?

Rich (BB code):
    5.0V      4.5V      3.3V      3V        2.2V      1.0V      0.0V
|         |         |         |         |         |         |
| V1=0.5v | V2=1.2v | V3=0.3v | V4=0.8v | V5=1.2v | V6=1.0v |
|         |         |         |         |         |         |
5V   o--/\/\/--+--/\/\/--+--/\/\/--+--/\/\/--+--/\/\/--+--/\/\/--o GND
R1        R2        R3        R4        R5        R6

I1 = I2 = I3 = I4 = I5 = I6 = 20ma

R1 = V1/I1 = 0.5/0.02 = 25Ω
R2 = V2/I2 = 1.2/0.02 =
R3 = V3/I3 = 0.3/0.02 =
R4 = V4/I4 = 0.8/0.02 =
R5 = V5/I5 = 1.2/0.02 =
R6 = V6/I6 = 1.0/0.02 =

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#### MrChips

Joined Oct 2, 2009
21,056
I don't quite see the difficulty. I must be missing something.

#### thatoneguy

Joined Feb 19, 2009
6,359
I don't quite see the difficulty. I must be missing something.
I'm not sure, either. Maybe it's for people new to Ohms law?

I was expecting a 10x10 grid of Resistors, with 10V on one corner, and Gnd on the opposite corner, and asked to find the voltage at point x,y in the grid.

#### wayneh

Joined Sep 9, 2010
16,390
...we haven't a clue about ohm's law, which forms the entire basis for electronics.
Hardly. Tell me how Ohm's law explains the output from my experimental alternator, versus RPM and applied load. Ohm's law is mute on inductance and a host of other "electronics" issues. Important? Yes. But I think Maxwell and others would beg to differ on the omnipotence of Ohm's law.

It is interesting that the historical importance of Ohm's law was in describing how voltage dropped in proportion to resistance. Other hypotheses at the time were that resistance to some power gave the right answer. Ohm suggested the power was exactly 1, and appears to have been correct, although at the time he was ridiculed for a "web of naked fancies".

#### CDRIVE

Joined Jul 1, 2008
2,219
This is an odd topic. Unless I'm misinterpreting your intentions, it would appear that your quizzing the membership to determine our qualifications. After all, you're post is more of a statement than a question.

#### justtrying

Joined Mar 9, 2011
429
what's the problem with I/R? seems to be straight forward enough.

Pretty sure I agree with MMcLaren in terms of the answer. I got a much more difficult test tomorrow so don't need any seeds of doubt about my competency with Ohm's Law

#### thatoneguy

Joined Feb 19, 2009
6,359
TIt would appear that your quizzing the membership to determine our qualifications.
I think it is having the opposite effect.

#### strantor

Joined Oct 3, 2010
5,226
Thing is, in mind it makes no sense that we are all talking about transistors and OP AMPs when we haven't a clue about ohm's law, which forms the entire basis for electronics.
who is we? the forum members or some people in your class?

#### thatoneguy

Joined Feb 19, 2009
6,359
who is we? the forum members or some people in your class?
Did you know you can still use a calculator with a "9" button that doesn't work?
Here's all you need to do whenever you need a 9:
$$8-e^{i\pi}$$

#### justtrying

Joined Mar 9, 2011
429
Did you know you can still use a calculator with a "9" button that doesn't work?
Here's all you need to do whenever you need a 9:
$$8-e^{i\pi}$$
fancy, i would just go $$8+1^0$$ ' cause then I don't need to enter into the complex mode. Now all I need is to figure out how to get crumbs from under my "k"...

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