# voltage divider

#### Alex1700

Joined Jan 12, 2020
106

#### Papabravo

Joined Feb 24, 2006
20,594
What is the current in R1-R4 according to Ohm's Law?

• Alex1700

#### Alex1700

Joined Jan 12, 2020
106
What is the current in R1-R4 according to Ohm's Law?
all is the same i1 = i2 = i3 = i4

#### DickCappels

Joined Aug 21, 2008
10,103
According to the drawing the voltage across V3 is V3. I guess I do not understand the question.

#### Ian0

Joined Aug 7, 2020
8,939
You know the voltage drop across R2 and R3 together.
What fraction of that figure do you think is the voltage drop across R3 on its own?

#### sghioto

Joined Dec 31, 2017
5,082
On my interpretation I see 5.6 volts across R2 and R3 looking at the meter.
5.6 volts divided by 4200 ohms = .00133 amps x R3 (3K) = 4 volts across R3.

#### Ian0

Joined Aug 7, 2020
8,939
Isn't this a thread that should be in the homework section?

• djsfantasi

#### Alex1700

Joined Jan 12, 2020
106
.00133 amps x R
On my interpretation I see 5.6 volts across R2 and R3 looking at the meter.
5.6 volts divided by 4200 ohms = .00133 amps x R3 (3K) = 4 volts across R3.
how to get 4.2k ohm?

#### Ian0

Joined Aug 7, 2020
8,939
Look carefully at the drawing. Which resistors add up to 4200Ω?

#### MrChips

Joined Oct 2, 2009
29,809
What is the voltage across R1?
Use Ohm’s Law.

#### Papabravo

Joined Feb 24, 2006
20,594

#### dl324

Joined Mar 30, 2015
16,111
May i know what is the voltage drop at V3 ?
We don't do homework. You need to show your best effort before we can offer direction.

Members - this is a voltage divider homework assignment... We're not supposed to do the homework (@sghioto) or give misleading advice (@Papabravo, @MrChips). Ohm's Law is not required. Current is not required. Voltage across R1 is not required.

What is the current in R1-R4 according to Ohm's Law?
On my interpretation I see 5.6 volts across R2 and R3 looking at the meter.
5.6 volts divided by 4200 ohms = .00133 amps x R3 (3K) = 4 volts across R3.
What is the voltage across R1?
Use Ohm’s Law.

#### ericgibbs

Joined Jan 29, 2010
18,213
Hi Guys,
This is a Homework assignment in the Homework Forum.
You are reminded that in the forum guidelines, we do not provide the answer to assignments, only help.

Moderation

#### dl324

Joined Mar 30, 2015
16,111
all is the same i1 = i2 = i3 = i4
Since you're just learning this stuff, it would be advisable for you to describe things clearly.

There is only one current in a series circuit. You could say $$I_{R1}=I_{R2}=I_{R3}=I_{R4}$$, but what you said could be confusing.

#### WBahn

Joined Mar 31, 2012
29,489
View attachment 300875
May i know what is the voltage drop at V3 ?
There are a couple of reasonable ways to come about it. One, indeed, is to look at it as being a voltage divider. But it's apparent that you don't understand how voltage dividers work, so even if you throw the right formulas at the problem and managed to get the right answer, your level of comprehension probably wouldn't be improved.

So, I would recommend coming at it from basics -- which you will know you comprehend reasonably well when you can confidently derive both the voltage divider and current divider equations and understand what conditions must be met in order for them to apply.

You have Ohm's Law, which says that the voltage ACROSS the resistance between two points divided by the current through that resistance equals the value of that resistance (i.e., V/I = R).

You know the voltage between two particular points. What is the total resistance on a path between those two points? What is the current along that path?

Once you have that, can you figure out how to use Ohm's Law again to find the voltage across R3? Remember, if you want the voltage across a path, all you need to know is the resistance along that path and the current through that path.

#### Papabravo

Joined Feb 24, 2006
20,594
We don't do homework. You need to show your best effort before we can offer direction.

Members - this is a voltage divider homework assignment...
View attachment 300902

We're not supposed to do the homework (@sghioto) or give misleading advice (@Papabravo, @MrChips). Ohm's Law is not required. Current is not required. Voltage across R1 is not required.

#### WBahn

Joined Mar 31, 2012
29,489
I think the comment stems from the TS's description that this is a "voltage divider problem" and, indeed, it is not necessary to apply Ohm's Law or determine any currents in order to get the answer from that perspective. But, as I noted above, while this may be true, I don't think taking this approach is in the best interest of the TS's understanding of the fundamentals. Instead, it will lead to the all-too-common approach of trying to memorize when to throw which memorized equation at a problem, hoping to use it in such a way as to get an answer that they hope is correct.

Your question elicited a response that indicates that the TS does understand that resistors in series all have the same current flowing through them. That's a good starting point. But it doesn't appear that they understand how to use the information given to determine the actual current, so that would appear to be a reasonable focus for the next step.

As for the question about the current in R1, I'm not sure what the thinking there was. It might have been a typo and meant to be R3, but that's just a guess.

#### MrChips

Joined Oct 2, 2009
29,809
If the TS can assert that the voltage across R1 is given by
V1 = I x R1

then that is an excellent starting point.

TS should then move on to V2, V3, and V4.

After that, it is simply algebra and solving simultaneous equations. TS does not have to invoke an understanding of voltage dividers.

#### dl324

Joined Mar 30, 2015
16,111
TS does not have to invoke an understanding of voltage dividers.
The title and text in the picture posted say it's a voltage divider exercise. When I was in school, if you were told to solve a problem a certain way and you solved it using a different method, 0 credit was awarded for not following directions; even if you arrived at the correct answer.

#### Papabravo

Joined Feb 24, 2006
20,594
...And how many angels can dance on the head of a pin? Pomposity, it seems, knows no bounds.