Step 1: Simplify the circuit using source transformation.
First, convert the 5A current source on the left with its parallel 6Ω resistor into an equivalent voltage source.
The voltage source value will be VL=I×R=5A×6Ω=30V.
Since the current source points downwards, the positive terminal of the voltage source will be at the bottom (towards ground), and the negative terminal will be towards node NL. So, it contributes −30V to node NL. This 30V source will be in series with the 6Ω resistor.
Similarly, convert the 3A current source on the right with its parallel 4Ω resistor into an equivalent voltage source.
The voltage source value will be VR=I×R=3A×4Ω=12V.
Since the current source points upwards, the positive terminal of the voltage source will be towards node NR, and the negative terminal will be at the bottom (towards ground). So, it contributes +12V to node NR. This 12V source will be in series with the 4Ω resistor.
The circuit now looks like this, with two main nodes NL and NR (assuming the bottom wire is ground 0V):
- From node NL to ground: A 3Ω resistor in parallel with a series combination of a 6Ω resistor and a −30V voltage source.
- From node NR to ground: A 3Ω resistor in parallel with a series combination of a 4Ω resistor and a +12V voltage source.
- Between nodes NL and NR: A 7Ω resistor (through which io flows), and a series combination of a 1Ω resistor and a 5V voltage source. The 5V source has its positive terminal towards NL (through the 1Ω resistor) and its negative terminal towards NR.
Step 2: Apply Kirchhoff's Current Law (KCL) at nodes NL and NR using nodal analysis.
KCL at node NL (sum of currents leaving the node is zero):
7ΩNL−NR+1ΩNL−(NR+5V)+3ΩNL+6ΩNL−(−30V)=0
7NL−NR+(NL−NR−5)+3NL+6NL+30=0
Multiply the equation by 42 (the least common multiple of 7,1,3,6) to eliminate fractions:
6(NL−NR)+42(NL−NR−5)+14NL+7(NL+30)=0
6NL−6NR+42NL−42NR−210+14NL+7NL+210=0
(6+42+14+7)NL+(−6−42)NR=0
69NL−48NR=0(EquationA)
KCL at node NR (sum of currents leaving the node is zero):
7ΩNR−NL+1ΩNR−(NL−5V)+3ΩNR+4ΩNR−12V=0
7NR−NL+(NR−NL+5)+3NR+4NR−12=0
Multiply the equation by 84 (the least common multiple of 7,1,3,4) to eliminate fractions:
12(NR−NL)+84(NR−NL+5)+28NR+21(NR−12)=0
12NR−12NL+84NR−84NL+420+28NR+21NR−252=0
(−12−84)NL+(12+84+28+21)NR+420−252=0
−96NL+145NR+168=0
−96NL+145NR=−168(EquationB)
Step 3: Solve the system of equations A and B.
From Equation A: 69NL=48NR⟹NL=6948NR=2316NR.
Substitute the expression for NL into Equation B:
−96(2316NR)+145NR=−168
−231536NR+145NR=−168
To combine the terms with NR, find a common denominator:
23−1536NR+145×23NR=−168
23−1536NR+3335NR=−168
231799NR=−168
1799NR=−168×23
1799NR=−3864
NR=−17993864V
Now, calculate NL:
NL=2316NR=2316×(−17993864)
NL=−23×179916×3864=−4137761824V
We can simplify NR and NL by noting that 1799=7×257.
NR=−7×2573864=−257552V
NL=2316×(−257552)=−25716×24=−257384V
Step 4: Calculate the current io through the 7Ω resistor.
The current io flows from node NL to node NR.
io=7ΩNL−NR
io=7Ω−257384V−(−257552V)
io=7−257384+257552A
io=7257552−384A
io=7257168A
io=257×7168A
io=25724A
The current io is 24/257A.
3 done, 2 left today. You're making progress.