PhysicsCBSE Class 12 · Sample paper, session 2026-27 · 2 marks · Very short answer

CBSE Class 12 Physics sample paper 2026-27: question 19

From the official CBSE sample question paper for 2026-27, section B, question 19, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q19 · 2 marks · Very short answerElectrostatic Potential and Capacitance

Two like charges +q and +q are placed at a distance d. What work must be done by an external agent to bring another charge +q from infinity to the midpoint of the line joining the two given charges?

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2026-27.

Hints

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

Hint 1

Work done to bring a charge from infinity equals charge × potential at the final point.

Hint 2

Potentials are scalars — just add the contributions from both charges.

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.

The midpoint is at distance $d /2$ from each charge.
½ mark
Potential due to one charge at the midpoint: $V_{1} = \frac{k q}{d /2} = \frac{2 k q}{d}$ , where $k = \frac{1}{4 π ε _{0}}$ .
½ mark
Net potential (scalar sum): $V = 2 \times \frac{2 k q}{d} = \frac{4 k q}{d}$ .
½ mark
Work done by external agent (potential at infinity = 0): $W = q V = \frac{4 k q ^{2}}{d} = \frac{q ^{2}}{π ε _{0} d}$ .
½ mark

Answer: W = 4kq²/d = q²/(πε₀d)

Where the marks are

Distance of midpoint from each charge = d/2 (½ mark)
Potential of one charge = 2kq/d (½ mark)
Total potential = 4kq/d (½ mark)
W = qV = 4kq²/d (½ mark)

Revise the chapter

Chapter: Electrostatic Potential and Capacitance (notes, formulas, where marks are lost and every past question)
Topic: Electric Potential and Potential Energy

Practise this chapterBoard-style questions from Electrostatic Potential and Capacitance, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2026-27: every question, by section.

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CBSE Class 12 Physics sample paper 2026-27: question 19

Hints

Step-by-step solution

Revise the chapter

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