Whats the resistance of these two circuits?

Question

Okay, I had to draw this one up since I can't exactly put it into words. Whats the resistance between nodes A and B for these two circuits? (Click link for picture.)

http://img247.imageshack.us/img247/3381/resistorssp2.jpg

Answer 1

1) You have a parallel group of R3 and a series of R1 and R2.

R123 = R12 * R3 / (R12+R3)

First find R12

R12 is a series of R1 and R2 so add them

R12 = R1 + R2

R12 = 100Ω + 220Ω = 320Ω

R123 = 320Ω * 400Ω / (320Ω + 400Ω) = 1600/9Ω = 177.77Ω ≈ 178Ω

2) You have a series of two parallel groups

The first parallel group is

R45 = R4 * R5 / (R4 + R5)

R45 = 1kΩ * 5kΩ / (1kΩ + 5kΩ) = 5/6 kΩ

The second parallel group is

R67 = R6 * R7 / (R6 + R7)

R67 = 3kΩ * 10kΩ / (3kΩ + 10kΩ) = 30/13 kΩ

Add the two groups because it is a series

R4567 = R45 + R67 = 5/6 kΩ + 30/13 kΩ = 245/78 kΩ ≈ 3.14kΩ

Answer 2

A: 1/R = 1/320 + 1/400

        320 * 400 = 720R;  R= 177.78ohms

B:  R = S + T

       1/S = 1/1k + 1/5k           S = 5k/6  =  0.83k

        1/T = 1/3k + 1/10k         T = 30k/13 = 2.3k

       R = 3.13k

Answer 3

For the first picture should be 177.7

For the second should be 3.13k

Answer 4

I'm pretty sure (if I remember Ohm's law correctly ) that the resistance of figure 1 is 360 ohms, and figure 2 would be 9.5k ohms

Answer 5

Hi there,

Have you try these equations?

R = R1 + R2 + R3 + ...

(for series circuit)

1 / R = 1 / R1 + 1 / R2 + 1 / R3 +...

(for parallel circuit)

I think it's simple enough for you to figure it out now.

Vote me Best Answer plzz!

Answer 6

1) R1 and R2 are in series, total is 320 ohms. This is in parallel with 400 ohms, total is 320*400/(320+400) = 178 ohms

2) 2 on left are 1*5/(1+5) = 833 ohms

2 on right are 3*10/(3+10) = 2300 ohms

total add the two = 3133 ohms

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