 Ask Remember Me? pop000 Posts: 352, Reputation: 6 Full Member #1 Nov 18, 2011, 07:41 AM
find the resistance of CD (Rcd)
in the picture you can what I did till I stuck.

NO.1 is the source, and NO.2 is after I found the equivalent resistance R-5,6,7 (which is in parallel).

but now I think R2 and R1 is also parallel but I am not sure.

all I know that is the final answer should be Rcd=3-ohm

thanks. ebaines Posts: 12,132, Reputation: 1307 Expert #2 Nov 18, 2011, 08:52 AM Originally Posted by pop000 in the picture you can what i did till i stuck.
Pop - you need to attach the figure. pop000 Posts: 352, Reputation: 6 Full Member #3 Nov 18, 2011, 08:59 AM
Oh again is happened sorry :)
Attached Images  ebaines Posts: 12,132, Reputation: 1307 Expert #4 Nov 18, 2011, 09:32 AM
The dead short can be thought of as a 0-ohm resistor in parallel with the 6 ohm. That makes the combination equivalent to 0 ohms. So now you have R2 and R1 in parallel, the combination of which is in series with R3.

I see that in figure 1 you have R2= 3 ohms, but in figure 2 you show R2 = 9 ohms. Which is it? pop000 Posts: 352, Reputation: 6 Full Member #5 Nov 18, 2011, 09:46 AM
"I see that in figure 1 you have R2= 3 ohms, but in figure 2 you show R2 = 9 ohms. Which is it?"

well in both R2=9ohm and R1=3ohm.where I show R2=3 ohm?

well so if you told that I have R2 and R1 in parallel, the combination of which is in series with R3.

so I get R:2,1=9*3/9+3=2.25-ohm,now we know is in series with R3 so we get 2.25+1.5=3.75-ohm

do I correct till here ? pop000 Posts: 352, Reputation: 6 Full Member #6 Nov 18, 2011, 09:52 AM
ohh yes yes now I see it, my mistake OK I solve it now.

so yes R2=3.

so I get R:2,1=3*3/3+3=1.5-ohm,now we know is in series with R3 so we get 1.5+1.5=3.00-ohm

so Rcd=3-ohm this is the final answer.

sorry for the confusion.

really thanks for your help :) ebaines Posts: 12,132, Reputation: 1307 Expert #7 Nov 18, 2011, 09:59 AM Originally Posted by pop000 well in both R2=9ohm and R1=3ohm.where i show R2=3 ohm?
You show R2 = 3 ohms in the upper (see attached snippet): Originally Posted by pop000 so i get R:2,1=9*3/9+3=2.25-ohm,now we know is in series with R3 so we get 2.25+1.5=3.75-ohm

do i correct till here ?
Yes. However, if R2 = 3 ohms then you fget a final answer of Rcd -= 3 ohms.
Attached Images  pop000 Posts: 352, Reputation: 6 Full Member #8 Nov 18, 2011, 11:24 AM
Yes you are correct it was my mistake :)

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