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Adding up resistors

by magnifik
Tags: adding, resistors
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magnifik
#1
Feb10-10, 03:25 PM
P: 361
1. The problem statement, all variables and given/known data



i'm a noob, and i am having trouble adding resistors. this circuit can be reduced to 1 resistor. what is its value?

2. Relevant equations
parallel: 1/Rtot=1/R1+1/R2+1/R3+1/R4
series: Rtot=R1+R2+R3+R4

3. The attempt at a solution
so i thought 3, 2, 2 added up in series and you just do 6/8+1/4, but this isn't right. =/ i'm having trouble discerning which resistors are parallel and which are in series. any help would be appreciated.
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willem2
#2
Feb10-10, 04:36 PM
P: 1,408
2 resistors R1 and R2 are in series if one connector of R1 is connected to a connector of R2 and nothing else is connected to these connectors. (or if you can determine that no current can flow through such a connection)

None of the resistors here is in series with any other.
The 3 ohm resistance isn't in series with any of the 2 ohm resistances because the point between the 3 ohm resistance and any of the 2 ohm resistances is also connected to the other 2 ohm resistance

2 resistors are parallels if one connector of R1 is connected to a connector of R2 and the other connector of R1 is connected to the other connector of R2. There's only 1 pair of
resistances here thats parallel.

The direction they are drawn in doesn't matter.

Once you combined those resistances, you can look again for a pair of resistances that is in series or parallel.
magnifik
#3
Feb10-10, 05:03 PM
P: 361
huh? so are you saying i can disregard the 3 Ohm resistor?
i know the answer is supposed to be 2. i don't know how to get there though.

willem2
#4
Feb10-10, 05:10 PM
P: 1,408
Adding up resistors

Quote Quote by magnifik View Post
huh? so are you saying i can disregard the 3 Ohm resistor?
i know the answer is supposed to be 2. i don't know how to get there though.
No. I said the 3 ohm resitor isn't in series with any of the 2 ohm resistances. What you have to do is find the pair of resistances that's parallel, combine those and then look for other series of parallel pairs
magnifik
#5
Feb10-10, 05:21 PM
P: 361
is 3 parallel with 4 and 2 is parallel with 2?


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