AL electric circuit
2011-02-02 7:52 am
圖片參考：http://imgcld.yimg.com/8/n/HA00265776/o/701102010153113873376380.jpg
The figure shows some of the resistors in a network resistors. The magnitudes and directions of some of the currents are marked as shown. Find the magnitude and direction of the current passing through the resistor R.
* Explain in detail
回答 (2)
2011-02-02 5:16 pm
✔ 最佳答案
The current flowing through the 1-ohm resistor = (0.3 - 0.2) A = 0.1 AVoltage across the 5-ohm resistor = 0.2 x 5 v = 1 v
Voltage across the 1-ohm resistor = 0.1 x 1 v = 0.1 v
Because the voltage drop across the 5-ohm resistor (1 v )is higher than that across the 1-ohm resistor (0.1 v), Current will flow from the lower end of the 3-ohm resistor to the upper end.
Current folwing through the 3-ohm resistor = (1 - 0.1)/3 A = 0.3 A
Let I be the current flowing throug the resistor R from right to left,
hence 0.3 = 0.1 + I
I = (0.3 - 0.1) A = 0.2 A
Therefore, a current of magnitude 0.2 A flows through R from right to left
2011-02-02 5:13 pm
By Kirchoff's first law, current through the 1 ohm resistor = 0.3 - 0.2 = 0.1 A
Hence voltage across the 5-ohm resistor = 1 V and across the 1-ohm resistor = 0.1 V
Thus, voltage across the 3-ohm resistor = 1 - 0.1 = 0.9 V, with the lower node being at a higher potential since the voltage drop across the 1-ohm resistor is less.
So current through the 3-ohm resistor = 0.9/3 = 0.3 A upward.
Hence by Kirchoff's first law again, current through R = 0.2 A to the left.
Hence voltage across the 5-ohm resistor = 1 V and across the 1-ohm resistor = 0.1 V
Thus, voltage across the 3-ohm resistor = 1 - 0.1 = 0.9 V, with the lower node being at a higher potential since the voltage drop across the 1-ohm resistor is less.
So current through the 3-ohm resistor = 0.9/3 = 0.3 A upward.
Hence by Kirchoff's first law again, current through R = 0.2 A to the left.
參考: 原創答案
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