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The effective resistance… (Class 12 Physics 2025, Q2)

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PhysicsCBSE Class 12 · Board exam 2025, set 55/7/1 · 1 mark · MCQ

CBSE Class 12 Physics 2025: question 2

Set in the CBSE Class 12 board exam of 2025, paper 55/7/1, section A, question 2, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q2 · 1 mark · MCQCurrent Electricity

The effective resistance between points A and B in the given circuit is :

  1. (A)
  2. (B)
  3. (C)
  4. (D)

Figure in the paper: Resistor network between terminals A (left) and B (right). A connects to a left node; B connects to a right node. Top path from A: 4 Ω up to a top-middle node via 2 Ω; top-middle node connects to the right node via 3 Ω then 6 Ω (down the right side). Top-middle node also connects to left node via 3 Ω, to right node via 18 Ω, and to a bottom node via a vertical 7 Ω. Bottom path: left node to bottom node via 4 Ω, bottom node to right node via 12 Ω. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2025 board paper, set 55/7/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

First combine resistors that are clearly in series.

Hint 2

Check whether the vertical 7 Ω branch is balanced, so that it can be ignored.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. Reduce the network step by step: combine resistors in series, then combine parallel pairs, and check whether the 7 Ω branch forms a balanced bridge (equal potential at its two ends, so it carries no current).

    ½ mark

  2. The reduced network gives an equivalent resistance of .

    ½ mark

Answer: 16/3 Ω, option (C)

Where the marks are

  • Correct reduction of the network to (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Current Electricity, one at a time, marked against the answer key and marking points.Back to the full paper2025 board paper, set 55/7/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.