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# le個circuit ge Resistance 點計

http://i684.photobucket.com/albums/vv203/GazeNoir/...

請問Total resistance across AB係幾多?

如果有1V across AB

咁中間個 Resistor ge Potential difference又係幾多?

可以ge話俾埋步驟我睇下

唔該晒

### 1 Answer

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- 六呎將軍Lv 71 decade agoFavorite Answer
Suppose when a voltage 1V is applied across AB, current flow is shown below:

圖片參考：http://i388.photobucket.com/albums/oo325/loyitak19...

So we can derive the equation as follows:

I1R + 2(I1 - I3)R = 1

3I1R - 2I3R = 1 ... (1)

2I2R + (I2 - I3)R = 1

3I2R - I3R = 1 ... (2)

(I1 + I3)R = 2I2R (Kirchoff's voltage law in the left loop)

I1R - 2I2R + I3R = 0 ... (3)

Solving, we have: I1 = 5/(9R), I2 = 4/(9R) and I3 = 1/(3R)

Therefore the current through the resistor in the middle = 1/(3R)

And total current drawn = I1 + I2 = 1/R

Hence the equivalent resistance = 1/(1/R) = R

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