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What is the current in the 4 Ω resistor when switch S₁ is open and switch S₂ is closed in the given circuit?

Asked in GUJCET 2017 · Kirchhoff's laws in networks

Figure: Kirchhoff's laws in networks
Answer: (4) 1.2 A

Step-by-step solution

Given (figure): an ideal 12 V battery with 4 Ω and 6 Ω in series; a 12 Ω branch containing S₁ is connected across the 6 Ω; S₂ is connected across the 5 Ω on the right.

S₁ open: no current can flow in the 12 Ω branch, so it drops out.

S₂ closed: a zero-resistance path is in parallel with the 5 Ω, so the 5 Ω is short-circuited and carries no current.

What remains is 4 Ω and 6 Ω in series: R = 10 Ω.

I = (12)/(10) = 1.2 A, the same through the 4 Ω and the 6 Ω.

Why the other options are wrong

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