Finding Missing R3 in Combination Circuit

Thread Starter

aeln269

Joined Oct 18, 2020
31
Screen Shot 2020-11-02 at 7.51.16 PM.png

Hi everyone, im stuck on this problem for my homework. What ive done so far is R3 = RT - R1 - R2 - R4. Also, the current total is supposedly 10ma
 

MrChips

Joined Oct 2, 2009
23,308
Step 1: What is the current flowing through R1?
Step 2: What is the voltage across R1?
Step 3: What is the voltage across R4?
Step 4: What is the current flowing through R4?
Step 5: What is the current flowing through R3?
Step 6: What is the voltage across R3?
Step 7: What is the resistance of R3?
 

Thread Starter

aeln269

Joined Oct 18, 2020
31
For #1, I= V/R right? Also because this is a parallel circuit, does that make all of the voltages the same? So is it also 10ma?
 

MrChips

Joined Oct 2, 2009
23,308
No. You cannot make that assumption until you work through it.

R1 is in parallel with R2.
What is the equivalent resistance of R1 and R2?
What is the voltage across R1?
What is the voltage across R2?
 

Thread Starter

aeln269

Joined Oct 18, 2020
31
Ok this is what I did.

because R1 and R2 are in parallel, I combined them to solve for R1R2

1/1000+1/1000

2/1000

1000/2

R1R2 = 500

Then I used ohms law V=IR

V=(10ma)(500)
V=0.01(500)
V=5

which applies for both because they are parallel?
 

Ramussons

Joined May 3, 2013
942
Maybe I should highlight my point.

From the values given in the figure, R3 cannot be determined.

The footnote is an addon.

...... Also, the current total is supposedly 10ma ....
 
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