Thevenin's Theorem 急!!*

2010-10-01 4:22 am

http://i409.photobucket.com/albums/pp172/momoko_deedee/elect_lab4.jpg

Rth係唔係479.53...?
Vth點搵...?

搵埋V4同I4最好!! 不過唔搵都OK...答左Rth同Vth都足夠><
超急...thx a bunch*

更新1:

唔該晒~~^^ 不過其實我仲有少少唔明:: Vth=V5?? 點決定搵邊個valtage ga? 係咪次次都用最近open circuit果個resistor的voltage? 雖然我自己都係用左mesh analysis,, 但ar sir話用nodal analysis好d.. 咁如果用nodal analysis的話, 第1條equation會係: -(Va-6)/470 + Va/1000 + (Va-Vb)/100 = 0 另外果條equation又係點..?? 要ignore R3嗎~? 萬分感激~~>

回答 (1)

天同

2010-10-01 8:50 am

✔ 最佳答案

470-ohm parallel with 1000-ohm = 470x1000/(470+1000) ohms =319.73 ohms
319.73 ohms in series with 100-ohms = (319.73+100) ohms = 419.73 ohms
419.73 ohms in parallel with 680 ohms = 419.73 x 680/(419.73+680) ohms = 259.53 ohms
259.53 ohms in series with 220 ohms = (259.53+220) ohms = 479.53 ohms

To find Thevenin voltage,6 = 470(I1) + 1000(I1-I2)and 1000(I1-I2) = (100+680)I2
solve for I2 gives I2 = 3.71x10^-3 A
Therefore, the Thevenin resistance is 479.53 ohms and Thevenin voltage is 680 x 3.71 x 10^-3 v = 2.52 v

Hence, I4 = 2.52/(330+479.53) A = 3.11x10^-3 AV4 = 3.11 x 10^-3 x 330 v = 1.03 v

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