- 2070 Asar (old course) · 8 marks
Nodal analysis: current in each branch
Short answer
With V1, V2, I2 = (V1−V2)/5, nodal analysis gives V1 = 4.25 V, V2 = 6.333 V, I2 = −0.4167 A. Branch currents: 3 Ω source branch 1.917 A, 2 Ω + dependent source 2.333 A, 5 Ω I2 = −0.417 A, 4 Ω 1.583 A.
Find the current in each branch of the following figure using nodal analysis. [Figure: 10 V source (+ at top) in series with a 3 Ω resistor feeding node N1. From N1: a 2 Ω resistor in series with a dependent voltage source of value I2 (+ at top) going down to the bottom wire; and a 5 Ω resistor carrying current I2 to node N2. From N2: a 4 Ω resistor to the bottom wire and a 2 A current source (arrow pointing up into N2) to the bottom wire.]
Assumptions from the figure: 10 V source (+ at top) with 3 Ω feeds node N1. From N1, the branch 2 Ω in series with a dependent voltage source of value I₂ volts (+ at top) goes to ground. A 5 Ω resistor carries I₂ from N1 to N2. At N2, a 4 Ω resistor goes to ground and a 2 A source pushes current into N2.
Nodal equations (V₁ at N1, V₂ at N2)
Control variable: I₂ = (V₁ − V₂)/5.
Node N2 (current in = current out):
I₂ + 2 = V₂/4
(V₁ − V₂)/5 + 2 = V₂/4 ... (1)
Node N1: current from source branch = current in 2 Ω branch + I₂. The 2 Ω branch current is I_b = (V₁ − I₂)/2:
(10 − V₁)/3 = (V₁ − I₂)/2 + I₂ ... (2)
Solving
From (1): I₂ = V₂/4 − 2, and V₁ = V₂ + 5I₂ = 2.25V₂ − 10.
Put in (2): 2(10 − V₁) = 3(V₁ + I₂) → 20 = 5V₁ + 3I₂
20 = 5(2.25V₂ − 10) + 3(V₂/4 − 2) = 12V₂ − 56
V₂ = 6.333 V
V₁ = 4.25 V
I₂ = 6.333/4 − 2 = −0.4167 A
Branch currents
| Branch | Current |
|---|---|
| 3 Ω (source branch) | (10 − 4.25)/3 = 1.917 A |
| 2 Ω + dependent source | (4.25 + 0.4167)/2 = 2.333 A |
| 5 Ω (I₂) | −0.4167 A (flows N2 to N1) |
| 4 Ω | 6.333/4 = 1.583 A |
| 2 A source | 2 A |
Check: 1.917 = 2.333 − 0.4167 at N1 ✓; 1.583 = 2 − 0.4167 at N2 ✓.
Answer: I(3 Ω) = 1.917 A, I(2 Ω) = 2.333 A, I₂ = −0.417 A, I(4 Ω) = 1.583 A.
✓ Answer checked by Claude Opus 5.5 (high effort)
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