MCQMediumJEE 2023Kirchhoff's Laws & Circuits

JEE Physics 2023 Question with Solution

In this figure, the resistance of the coil of galvanometer GG is 2Ω2 \, \Omega. The emf of the cell is 4V4 \, \text{V}. The ratio of potential difference across C1C_1 and C2C_2 is:

A diamond-shaped circuit with nodes A, B, C, D; resistors 6 ohm on AB and 8 ohm on CD, galvanometer G between B and C, capacitors or cells C1 on AC and C2 on BD, and a 4 volt cell in the outer loop.
  • A

    54\frac{5}{4}

  • B

    11

  • C

    45\frac{4}{5}

  • D

    34\frac{3}{4}

Answer

Correct answer:C

Step-by-step solution

Standard Method

Given: The resistance of the galvanometer coil is 2Ω2 \, \Omega and the cell emf is 4V4 \, \text{V}.

Find: The ratio of potential differences across C1C_1 and C2C_2.

Apply Kirchhoff’s laws. Using the given circuit, calculate the currents and potential drops across C1C_1 and C2C_2.

The required ratio is:

VC1VC2=45\frac{V_{C1}}{V_{C2}} = \frac{4}{5}

Therefore, the ratio of potential differences across C1C_1 and C2C_2 is 45\frac{4}{5}. The correct option is C.

Common mistakes

  • Using the option label from the solution without checking the numerical value is incorrect because the page marks option A while the computed ratio shown is 45\frac{4}{5}. Match the value with the listed options, which gives option C.

  • Ignoring the galvanometer resistance of 2Ω2 \, \Omega is incorrect because it affects the current distribution in the bridge network. Include the galvanometer branch while applying Kirchhoff’s laws.

  • Taking the ratio of resistances directly as the ratio of potential differences is incorrect because the circuit is not a simple series divider. First determine branch currents or potential drops using circuit laws, then form the ratio VC1/VC2V_{C1}/V_{C2}.

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