AtomSoft

I learned this from http://www.bcae1.com/resistrs.htm
I know some true nooBs would like this info so i decided to post it again

How to calculate voltage drop across series resistors.

Step 1: Determine Current of total resistors across the series.
(I = Current/V=Voltage/R(t)=Resistance Total)
I = V / R(t)
I = 9 / (2k + 5k + 10K)
I = .53 mA

Step 2: Now that we have the Current across the resistors we can calculate the voltage across EACH resistor.
I = Current
Vx=Voltage (x=Current Value across X Resistor)
Rx=Resistor value(x=resistor#)

V = I x Rx

V1 = .53 mA x 2k
V1 = 1.06V

V2 = .53 mA x 5k
V2 = 2.65

V3 = .53 mA x 10k
V3 = 5.3V

V1 + V2 + V3 = 9.01 (voltage is 9V only 9.01 because i rounded up from .529 to .53) At .529 you can see barely a difference:

V1=1.058V
V2=2.645V
V3=5.290V
V Total= 8.993V

Also If the resistors are all the same value its easier.

So just add them up:

I = V / R(t)
I = 9 / (5k + 5k + 5K)
I = .6 mA

THEN:


V = I x Rx

V1 = .6 mA x 5k
V1 = 3V
so since all Resistors are same value:
V2 = 3V
V3 = 3V

Also To get different values for like switches just use gnd as a start point and the end of each resistor and a end point. This way you get 3 switches from this each having different voltages

SW1 = 3V
SW2 = 6V
SW3 = 9V

So I hope someone can learn something from this.

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FITNAH

Thank for posting this, Im quite beside myself with being dejected for being to stupid .
Im trying to figure out how to figure the voltage drop over to resistors.
The example Im using is a DC circuit
V=25
R1=3.3
R2=2.5
I =6.3
I told ( according to an quiz) that the voltage drop @ R1 is described as 21V
and R2 as 14
I have know idea how to come up with those values.
Any insight would be greatly appreciated.

Rolf

Ohms law says that E/R=I, so I should be 4.31A
So if E= IxR what do you get?

FITNAH

34.65a.
I get 6.36 for I ,dividing the combined resistance into V.
which then in turn gives me a voltage drop of 20.79 =R1 and 15.75 =R2
which also doesn't add up to 35 the original answer.

Rolf

How can 25v/5.8 ohm be anything but 4.31A?

FITNAH

Sorry typo, the model I have here is V =35
4.54 is of course correct, sorry about being sloppy.

FITNAH

I already feel like quit the idiot over not knowing how to find this answer and now flubbing the question hasn't helped,
In any case their must be a formula for finding the voltage drop over two or more resistors of different values

Nigel Goodwin

Ohms law and a little thought!.

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FITNAH

Thanks, the voltage drop across the resistors must add up to the voltage correct?

Nigel Goodwin

For a start draw the circuit and post it here!.

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FITNAH

Oh this is to embarrassing,
I glad it happened here before any classes started I haven't been in school for 20 years.
I went back to find the problem and to my relief I found, Im still an idiot, just not the kind I was beginning to believe I was.
I had mistake when I copied the problem off the internet, then went about trying to get the right answer with the wrong numbers.

This has been a very good lesson for me.

Take your time check what you are doing and pay attention .
R2 is 2.2
not 2.5.

Ambient

Copying errors cause a lot of problems. Make sure you read over the entire problem on tests, too. That caused me a lot of headaches.

FITNAH

Thanks I'm now in class and doing well.

AtomSoft

Im glad to see this was helpful.

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