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Saturday, 31 October

JEE Main 2021 · PhysicsMultiple choiceSingle correctEasyConceptual

JEE Main 25 July 2021, Shift 2, Physics Q11

Question 11 of 90 in this shift, Physics question 11 of 30, Section A.

If qfq_f is the free charge on the capacitor plates and qbq_b is the bound charge on the dielectric slab of dielectric constant kk placed between the capacitor plates, then bound charge qbq_b can be expressed as :
  1. (1)qb=qf(1−1k)q_b = q_f\left(1 - \frac{1}{k}\right)Official answer
  2. (2)qb=qf(1−1k)q_b = q_f\left(1 - \frac{1}{\sqrt{k}}\right)
  3. (3)qb=qf(1+1k)q_b = q_f\left(1 + \frac{1}{k}\right)
  4. (4)qb=qf(1+1k)q_b = q_f\left(1 + \frac{1}{\sqrt{k}}\right)

Official answer

Option 1

NTA final key.

Same idea in other shifts

Asked 2× in all
  1. 7 Apr 2025, Shift 2 · Q49A parallel plate capacitor has charge 5×10−65\times10^{-6} C. A dielectric slab is inserted between the plates and almost fills the space…MediumNumerical 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. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.