# Calculating Unknown Resistor in a parallel circuit.?

Thread Starter

#### Lewis Miller

Joined Oct 29, 2011
3
Thread Starter

#### Lewis Miller

Joined Oct 29, 2011
3
Help anybody? Please! I will get in trouble, I know it's my own fault etc but we need to work together!

#### praondevou

Joined Jul 9, 2011
2,942
Isn't there some data missing? Where is this exercise from?

Thread Starter

#### Lewis Miller

Joined Oct 29, 2011
3
Exercise is from Electrical & Electronic Principles Q 1.b Extended National Diploma / Diploma

#### praondevou

Joined Jul 9, 2011
2,942
Sorry, I didn't read your question correctly.

Start by calculating the voltage drop on R1. (current is 6Amps you wrote)
Then calculate the total resistance of R1 R2 R3.
Then use the voltage drop of R1 and the total resistance of R1 R2 R3 to calculate the total current.

Then calculate the voltage drop on R5. This gives you the partial current of R5 and therefore the partial current of R111111.
With the voltage drop on R111111 and it's current known you calculate it's resistance.

Edit: Oops, I think you meant 6Amps total current, right? In this case calculate the total resistance of R1 R2 R3, this will give you the voltage drop on them. The voltage drop on R6 is also known, since you have the current through it.

Substract the two voltage drops from the main voltage so you have the voltage drop on R5||R11111. From there it's the same thing