Newbie electronic resistance question

The answer given for question 5 IS correct.

Please post on newsgroup sci.electronics.basics

...Jim Thompson

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Jessie, newbie questions should be asked in

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Michael A. Terrell
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In multiple choice questions where you have no clue as to what they are on about, always pick the longest answer.

Best regards, Spehro Pefhany

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Im not going to bother with the link just yet, im going to help you with why you should learn ohms law. Actually you shouldnt learn ohms law you should understand electricity and in turn come to understand ohms law, it should just be 'common sense'. If you want some examples with why you would need it. You want to save money by using the smallest resistor possible. What do you need .25 watt .5 watt or 1 watt or 5 watt well if you know the voltage and the resistance you can figure out current and with the current and the voltage you can thus figure out wattage watts=volts*amps or watts =resistance*voltage squared or you have an analog to digital converter that will only take 5 volts but your signal goes up to 12 volts. What do you do, have no fear, for ohms law is here! use a voltage divider and knock that voltage down divide by 4 now your giving your a/d 3 volts not 12 see it comes in handy what you should be doing is studying whats a volt, whats an amp, whats inductance, whats capacitance whats resistance and in doing so ohms law will become "like yeah DUH i didnt need them to tell me that"

C.

You have to essentially work from the inside, outward. Solve the easiest bits first, and build your way up to the final circuit. The previous questions are designed to give you this skill.

There are obviously three resistors in parallel (2,3,5ohm), so solve them first, that gives 0.9677ohms

Next solve the two resistors in series, 10ohm + 12ohm = 22ohm

Now you'll notice that the 3 resistors you solved first are in parallel with the two series ones you solved second, so solve 0.9677ohms in parallel with 22ohms, that's 0.9269ohms.

This total value of 0.9269ohms is then clearly in series with the 3 ohms resistor on the right. So 3 + 0.9269 = 3.9269ohms

Hope that helps.

Dave :)

yes that helps immensily. I was way out there using the resister on the right as a series with the middle resister in the center and all other sorts of lunacy. Now i see where i was wrong in so many situations thanks a lot.

for now on ill take everyones advice and post in the .basic newsgroup (this was the first one that google came up with :/ ) Ill be posting here soon enough though ;)

thanks again

Jesse

Great! Now it's time to move onto the famous resistor cube problem:

*evil grin*

Dave :)

In message , dated Tue, 1 Aug 2006, ragtag99 writes

You should post to sci.electroncis.basics which is specially for helping new people.

What answers do you get? That may help to detect where you are going wrong.

The three low-value resistors in parallel are 2 ohms, 3 ohms and 5 ohms. Maybe you misread the values.

The way to calculate the total resistance in your head is not to use directly the formula 1/R = 1/R1 + 1/R2 + 1/R3 but an equivalent:

2 x 3 x 5 = 30. 2 ohms = 30/15, so 1/(2 ohms) = 15/30. Similarly, 1/(3ohms) = 10/30 and 1/(5 ohms) = 6/30.

Then 15/30 + 10/30 + 6/30 = 31/30. This is 1/R, so R = 31/30 ohms.

Then the series branch: 10 ohms + 12 ohms = 22 ohms.

22 ohms in parallel with 31/30 ohms: Work in the same way as for the three resistors: 22 x 30 = 660. 30/660 + (31 x 22)/660 = 712/660, so the resistance is 660/712 = 0.927 ohms (use calculator)

Add the 3 ohms in series to get the total resistance = 3.927 ohms.

I can understand that view. The trouble is that you need to learn more about practical circuits before you could understand why and how Ohm's Law is used. Some examples on the web page, especially fig 3, rarely come up in real life.

You are way off. Sorry.

>

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In message , dated Tue, 1 Aug 2006, leeps writes

The mind boggles. DON'T, whatever you do, EVER get a teaching or training job.

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Actually i do a pretty good job when the person is in front of me. But yeah i agree after i read what i wrote i know i didnt do much help. I hope at the very least he'll take my advice and look up the voltage, amperage , etc instead of just learning ohms law cause thats what your supposed to do

In message , dated Wed, 2 Aug 2006, leeps writes

English may not be your first language but you write it as if you know it well. So why not go the further step of punctuating properly and writing 'I' instead of 'i'?

You give the impression of semi-literacy.

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OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
2006 is YMMVI- Your mileage may vary immensely.

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

Amperage?

Is that the amount of '&' per line?

or did you mean current?

;)

PeteS

In message , dated Wed, 2 Aug 2006, PeteS writes

No, that's 'ampersandwich'

He's just paying ohmage to technician-speak.

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OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
2006 is YMMVI- Your mileage may vary immensely.

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

I suppose I deserve it. The thing is i grew up in the states and spent the last two years in france and i hate to say it im forgetting some of my english. im actually starting to put the adjective after the noun sometimes when i speak english ill say things like food hot or girl blond. Its actually starting to scare me. but hey give a guy a break im trying to help

One of my pet peeves as well!

I didn't think you were supposed to pet peeves?

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Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Watch out, they might bite,especially when they have been estivating.

You got the answer to your other question.

A practical example is putting a resistor in series with an LED, so that you won't burn the LED out. Say you have a typical LED, which has a maximum current rating of 30 mA, and you want to light it from a 9 volt battery. The LED uses 1.8 volts, so you need to drop

7.2 volts in the resistor. E=IR, so 7.2 = .03 R, therefore R = 7.2/.03 or 240 ohms.

Ed

Would it be