Learn

Friday, 9 October

JEE Main 2025 · PhysicsMultiple choiceSingle correctMediumMulti-step

JEE Main 2 April 2025, Shift 1, Physics Q34

Question 34 of 75 in this shift, Physics question 9 of 25, Section A.

A small bob of mass 100 mg and charge +10 μC+10\ \mu\mathrm{C} is connected to an insulating string of length 1 m. It is brought near to an infinitely long non-conducting sheet of charge density 'σ\sigma' as shown in figure. If string subtends an angle of 45∘45^\circ with the sheet at equilibrium the charge density of sheet will be. (Given, ϵ0=8.85×10−12 Fm\epsilon_0=8.85\times10^{-12}\ \frac{\mathrm{F}}{\mathrm{m}} and acceleration due to gravity, g=10 ms2g=10\ \frac{\mathrm{m}}{\mathrm{s}^2})

The figure, in words

Vertical infinite sheet with positive charge density +sigma (row of + signs); string of length l = 1 m attached at point A on the sheet, making 45 degrees with the sheet, with a bob of charge +10 microcoulomb at its lower end, away from the sheet.
  1. (1)1.77 nC/m21.77\ \mathrm{nC/m^2}Official answer
  2. (2)0.885 nC/m20.885\ \mathrm{nC/m^2}
  3. (3)17.7 nC/m217.7\ \mathrm{nC/m^2}
  4. (4)885 nC/m2885\ \mathrm{nC/m^2}

Official answer

Option 1

NTA final key.

Chapter
Electric Charges and Fields
Topic
Electric Field
Idea tested
Field of an Infinite Non-Conducting Sheet

Same idea in other shifts

Asked 2× in all
  1. 29 Jan 2024, Shift 1 · Q55An electron is moving under the influence of the electric field of a uniformly charged infinite plane sheet S having surface charge…HardNumerical value

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. This question needs a figure we do not reproduce; it is described in words above. Lumi analyses 42 of the 174 JEE Main shifts held from 2017 to 2026.