help me pls !!
how to find the total resistance ??

 

Start by solving the parallel resistances first then simplify until you are forced to solve for parallel again and so on.

 

babyboyx --

If it's R8 that is confusing you. Get rid of it. It doesn't need to be there, it's shorted.

Now calculate
\(\fra{1}{\fra{1}{R4}+\fra{1}{R5}}\) call it Ra --Parallel Connection calculation

\(\fra{1}{\fra{1}{R6}+\fra{1}{R7}}\) call it Rb --Parallel Connection calculation

Calculate
R3+Ra+Rb call it Rc --Series Connection Calculation

Calculate
\(\fra{1}{\fra{1}{R2}+\fra{1}{Rc}}\) call it Rd -- Parallel Connection Calculation

Calculate
R1+Rd call it Rtotal -- Series Connection Calculation

Z

 

babyboyx --

If it's R8 that is confusing you. Get rid of it. It doesn't need to be there, it's shorted.

Now calculate
\(\fra{1}{\fra{1}{R4}+\fra{1}{R5}}\) call it Ra --Parallel Connection calculation

\(\fra{1}{\fra{1}{R6}+\fra{1}{R7}}\) call it Rb --Parallel Connection calculation

Calculate
R3+Ra+Rb call it Rc --Series Connection Calculation

Calculate
\(\fra{1}{\fra{1}{R2}+\fra{1}{Rc}}\) call it Rd -- Parallel Connection Calculation

Calculate
R1+Rd call it Rtotal -- Series Connection Calculation

Z

Going forward plug in
\(\fra{1}{\fra{1}{R2}+\fra{1}{Rc}}\) for RD to get...

\(R1+\fra{1}{\fra{1}{R2}+\fra{1}{Rc}}\) Then plug in

R3+Ra+Rb for Rc to get...

\(R1+\fra{1}{\fra{1}{R2}+\fra{1}{R3+Ra+Rb}}\) then plug in...

\(\fra{1}{\fra{1}{R4}+\fra{1}{R5}}\) for Ra and

\(\fra{1}{\fra{1}{R6}+\fra{1}{R7}}\) for Rb to get...

\(R1+\fra{1}{\fra{1}{R2}+\fra{1}{R3+\fra{1}{\fra{1}{R4}+\fra{1}{R5}}+\fra{1}{\fra{1}{R6}+\fra{1}{R7}}}}\)

 

ya it really confuse me the R8 ...
but now thx guys =]

 

btw if i wanna find the current across R2 need use total current ??
or just total voltage/R2 ??

 

You have to calculate the resistance of the network formed by R4,R5,R6,R7, and R8, lets call it Ra. That resistance is in parallel with R2. Calculate the total resistance of Ra ║R2 , and use that to calculate voltage across R2. Gravy.

 

mean that i have to use the R2 own voltage right ??
btw din R3 also parella wif R2 ??

 

No, you have to break every problem into it parts and solve all the parts. R2 is in parallel with a bunch of other resistors. Solve the other resistors first, then work on R2 and the other resistors in parallel together, turn them into one resistor. This (║) means parallel to.

Once you know the voltage across R2 (and the rest) you can solve the problem you're after.