NVAMediumJEE 2025Kirchhoff's Laws & Circuits

JEE Physics 2025 Question with Solution

The net current flowing in the given circuit is _____ A.

Circuit with a 2 V source on the left and top branch resistors 2 ohm, 2.5 ohm, capacitor 1 microfarad, and 1 ohm, with shunt resistors 4 ohm, 3 ohm, 6 ohm, 5 ohm, 8 ohm, and 4 ohm connected to the bottom rail.

Answer

Correct answer:1

Step-by-step solution

Standard Method

Given: A circuit with a 2V2 \, \text{V} source and the shown resistor network.

Find: The net current flowing in the circuit.

From the provided solution, first reduce the parallel resistor groups:

1R1=14+13=712\frac{1}{R_1} = \frac{1}{4} + \frac{1}{3} = \frac{7}{12}

so

R1=127Ω1.71ΩR_1 = \frac{12}{7} \, \Omega \approx 1.71 \, \Omega1R2=12.5+16=1730\frac{1}{R_2} = \frac{1}{2.5} + \frac{1}{6} = \frac{17}{30}

so

R2=3017Ω1.76ΩR_2 = \frac{30}{17} \, \Omega \approx 1.76 \, \Omega1R3=18+14=38\frac{1}{R_3} = \frac{1}{8} + \frac{1}{4} = \frac{3}{8}

so

R3=83Ω2.67ΩR_3 = \frac{8}{3} \, \Omega \approx 2.67 \, \Omega

Then add the series resistances as written in the solution:

Rt=2+1.71+1.76+6+1+2.67+5=20.14ΩR_t = 2 + 1.71 + 1.76 + 6 + 1 + 2.67 + 5 = 20.14 \, \Omega

Using Ohm's law,

I=VRI = \frac{V}{R}

with V=2VV = 2 \, \text{V},

I=220.140.099AI = \frac{2}{20.14} \approx 0.099 \, \text{A}

The same the solution also explicitly lists Correct Answer: 1 and states that this aligns with the accepted answer format. Therefore, taking the solution, the numerical answer is 11.

Discrepancy Noted from the solution

Given: the solution contains two inconsistent conclusions.

Find: The answer to be recorded.

Approach Solution - 1 calculates

I0.099A0.1AI \approx 0.099 \, \text{A} \approx 0.1 \, \text{A}

and its conclusion says the net current is 0.1A0.1 \, \text{A}.

However, the solution explicitly shows Correct Answer: 1, and Approach Solution - 2 also states the net current is 1A1 \, \text{A}.

Because the There is a clear discrepancy on the solution's between the numerical working and the listed final answer.

Common mistakes

  • Treating all resistors as directly in series is incorrect because several branches are shunt connections between the same two nodes. First identify which resistors are in parallel, then reduce the network step by step.

  • Ignoring the contradiction in the source solution can lead to recording the wrong numerical answer. The working gives about 0.1A0.1 \, \text{A}, but the page explicitly marks 11 as correct; for extraction, the declared correct answer on the solution must be used.

  • Using Ohm's law before finding the equivalent resistance is wrong. You must first simplify the resistor network to obtain RtotalR_{\text{total}}, and only then compute current using I=VRI = \frac{V}{R}.

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