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Saturday, 31 October

JEE Main 2021 · PhysicsNumerical answerNumerical valueHardCalculation

JEE Main 17 March 2021, Shift 2, Physics Q25

Question 25 of 90 in this shift, Physics question 25 of 30, Section B.

Seawater at a frequency f=9×102f=9\times10^{2} Hz, has permittivity ε=80ε0\varepsilon=80\varepsilon_0 and resistivity ρ=0.25 Ω\rho=0.25\ \Omegam. Imagine a parallel plate capacitor is immersed in seawater and is driven by an alternating voltage source V(t)=V0 sin(2πft)\mathrm{V(t)=V_0\ sin(2\pi}ft\mathrm{)}. Then the conduction current density becomes 10x10^{x} times the displacement current density after time t=1800\mathrm{t}=\frac{1}{800}s. The value of xx is ____________. (Given : 14πε0=9×109 Nm2C−2\frac{1}{4\pi\varepsilon_0}=9\times10^{9}\ \mathrm{Nm^2C^{-2}})

Official answer

6

NTA final key.

Chapter
Electromagnetic Waves
Topic
Parallel Plate Capacitors
Idea tested
Displacement Current Between Plates

Same idea in other shifts

Asked 7× in all
  1. 5 Apr 2026, Shift 1 · Q37A displacement current of 4.0 A can be set up in the space between two parallel plates of 6 μ6\ \muF capacitor. The rate of change of…EasySingle correct
  2. 7 Apr 2025, Shift 1 · Q26If ϵ0\epsilon_0 denotes the permittivity of free space and ΦE\Phi_E is the flux of the electric field through the area bounded by the…MediumSingle correct
  3. 5 Apr 2024, Shift 1 · Q45An alternating voltage of amplitude 40 V and frequency 4 kHz is applied directly across the capacitor of 12 μF12\ \mu\mathrm{F}. The maximum…EasySingle correct
  4. 1 Feb 2024, Shift 1 · Q44A parallel plate capacitor has a capacitance C = 200 pF. It is connected to 230 V ac supply with an angular frequency 300 rad/s. The rms…MediumSingle correct
  5. 29 Jun 2022, Shift 2 · Q56The displacement current of 4.425 μA\mu A is developed in the space between the plates of parallel plate capacitor when voltage is…MediumNumerical value
  6. 4 Aug 2021, Shift 2 · Q28The voltage between the plates of a capacitor of capacitance 5μF5\mu\mathrm{F} is changing at a rate of…EasyNumerical 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.