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Question #42827

Difficulty: 8/10 | 🟢 Free

The Question

A particle of mass mm and charge +q+q is constrained to move along a frictionless, non-conducting straight wire aligned with the xx-axis. The setup is permeated by an external electric field given by E⃗=E0(2xL−x2L2)i^\vec{E} = E_0 \left( \frac{2x}{L} - \frac{x^2}{L^2} \right) \hat{i}, where E0E_0 and LL are positive constants. The entire wire assembly is placed inside a rocket that accelerates along the positive xx-axis with a constant acceleration a0=3qE04ma_0 = \frac{3 q E_0}{4 m}. In the reference frame of the rocket, the particle is released from rest at a position slightly displaced from its stable equilibrium point. Determine the position of the stable equilibrium point xeqx_{eq} and the angular frequency ω\omega of its small oscillations.

Options

  • A.

    xeq=3L2,  ω=qE0mLx_{eq} = \frac{3L}{2}, \; \omega = \sqrt{\frac{q E_0}{m L}}

  • B.

    xeq=L2,  ω=qE0mLx_{eq} = \frac{L}{2}, \; \omega = \sqrt{\frac{q E_0}{m L}}

  • C.

    xeq=2L,  ω=2qE0mLx_{eq} = 2L, \; \omega = \sqrt{\frac{2 q E_0}{m L}}

  • D.

    xeq=3L2,  ω=3qE04mLx_{eq} = \frac{3L}{2}, \; \omega = \sqrt{\frac{3 q E_0}{4 m L}}

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Intuition_Breaker

Train your brain to resist "obvious" answers that are designed to deceive your intuition.

Concepts Behind This Question

Electric Field Line Geometry|Equilibrium Stability|Pseudo Force Directionality

Why This Question Is Tricky

Common Mistakes

This question tests the student's ability to analyze equilibrium and stability in a non-inertial reference frame.

A common trap is to either ignore the pseudo force entirely (leading to the purely electrostatic equilibrium at x=2Lx=2L) or to find the first root of the effective force equation (x=L/2x=L/2) and blindly assume it is stable without performing the second derivative test on the effective potential.

Because the electric field magnitude decreases after x=Lx=L, students relying purely on electrostatic intuition fail to realize that the constant pseudo force overtakes the weakening electric force, creating a stable potential well at x=3L/2x=3L/2 where the net force gradient is negative.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterElectric Charges and Fields - Class 12
ConceptElectric Field Line Geometry
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree