# Parallel and series circuit

#### phantomvs

Joined Jan 19, 2016
39
I am looking at trying to understand how to find the amps of R3 in the following attached circuit.

The voltage at R3 is 84 volts.

And the answer is the amps at R3 is 12. How do they get that ?

Thanks !

#### WBahn

Joined Mar 31, 2012
25,928
If the voltage across R3 is 84 V, what is the total voltage across the rest of the circuit?

#### phantomvs

Joined Jan 19, 2016
39
Well if i look at the circuit its 120 volts.

What i don't understand is how they get 12 amps on r3 #### WBahn

Joined Mar 31, 2012
25,928
You have 120 V across the total circuit, but you drop 84 V of that over R3. So how much is left to be dropped over the parallel combination of R1 and R2 plus the parallel combination of R4 and R5?

#### phantomvs

Joined Jan 19, 2016
39
What i don't get is that they just say 84v when they probe R3 , but i don't even have the ohm value of R3.

I am really stumpted on how they get 12 amps on R3 as an answer.

I

#### joepdon

Joined Jan 19, 2016
10
If you subtract the voltage drop from R3 from the total voltage you get 36V which is left for the rest of the resistors. This means you need to add up the rest of the resistors which comes out to be 3 ohms. Next you plug this information into v=ir. 36v=i*3ohms thus resulting in i=12amps. You can do this since the current of a component in series with the rest of the circuit is the total current since current only splits between parallel components.

#### djsfantasi

Joined Apr 11, 2010
6,531
@joepdon There are different rules in the Homework Help forum. While addressed to Thread Starter's, you might get some insight by reading Posting to the Homework Help Forum

Basically, the expectation is the TS does the work with guidance from members. Remember, it is the "Homework Help" forum, not the "Homework Done for You" forum.

#### joepdon

Joined Jan 19, 2016
10
@joepdon There are different rules in the Homework Help forum. While addressed to Thread Starter's, you might get some insight by reading Posting to the Homework Help Forum

Basically, the expectation is the TS does the work with guidance from members. Remember, it is the "Homework Help" forum, not the "Homework Done for You" forum.
Sorry about that, thanks for letting me know. I will read that now.

• absf

#### phantomvs

Joined Jan 19, 2016
39
thanks joepdon, it helped me as i figured it out.

didn`t mean to get anyone in trouble.

#### djsfantasi

Joined Apr 11, 2010
6,531
No ones in trouble here

You are both new members, and are just learning how the forums work.

Welcome to AAC!