An electric dipole of length 2 cm is placed at an angle of 30° with an electric field 2 × 10^5 N/C. If the dipole experiences a torque of 8 × 10^-3 Nm, the magnitude of either charge of the dipole, is (A) 4 μC (B) 7 μC (C) 8 mC (D) 2 mC

PhysicsCBSE Class 12 · Board exam 2023, set 55/5/1 · 1 mark · MCQ

CBSE Class 12 Physics 2023: question 1

Set in the CBSE Class 12 board exam of 2023, paper 55/5/1, section A, question 1, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q1 · 1 mark · MCQElectric Charges and Fields

An electric dipole of length 2 cm is placed at an angle of $3 0^{\circ}$ with an electric field $2 \times 1 0^{5}$ N/C. If the dipole experiences a torque of $8 \times 1 0^{- 3}$ Nm, the magnitude of either charge of the dipole, is

(A)4 μC
(B)7 μC
(C)8 mC
(D)2 mC

Source: official question paper from cbse.gov.in (PDF). See it in the full 2023 board paper, set 55/5/1.

Hints

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

Hint 1

Write the torque on a dipole in a uniform field.

Hint 2

Dipole moment p = q × (2a); solve for q with sin 30° = 0.5.

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.

Torque $τ = pE sin θ = q (2 a) E sin θ$ , so $q = \frac{τ}{2 a E sin θ}$ .
$q = \frac{8 \times 1 0 ^{- 3}}{0.02 \times 2 \times 1 0 ^{5} \times 0.5} = 4 \times 1 0^{- 6}$ C $= 4 μ$ C, option (A).
1 mark

Answer: 4 μC, option (A)

Where the marks are

Uses $τ = q d E sin θ$ and gets 4 μC (1 mark)

Revise the chapter

Chapter: Electric Charges and Fields (notes, formulas, where marks are lost and every past question)
Topic: Electric Dipole

Practise this chapterBoard-style questions from Electric Charges and Fields, one at a time, marked against the answer key and marking points.Back to the full paper2023 board paper, set 55/5/1: every question, by section.

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CBSE Class 12 Physics 2023: question 1

Hints

Step-by-step solution

Revise the chapter

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