Start Learning Free

Before You Begin

Question #42757

Difficulty: 8/10 | 🟢 Free

The Question

A rigid symmetric dipole is modeled as a symmetric top with moment of inertia I3I_3 about its symmetry axis and I1I_1 about any transverse axis passing through its center of mass. The dipole has a permanent electric dipole moment p⃗\vec{p} directed along its symmetry axis. It is placed in a uniform electric field E⃗\vec{E} directed along the positive Z-axis. Initially, the symmetry axis of the dipole is held at an angle θ0=60∘\theta_0 = 60^\circ with respect to the Z-axis. The dipole is given an initial spin angular velocity ω3\omega_3 about its symmetry axis such that I32ω32I1=72pE\frac{I_3^2 \omega_3^2}{I_1} = \frac{7}{2} p E (where p=∣p⃗∣p = |\vec{p}| and E=∣E⃗∣E = |\vec{E}|), and then released such that its initial nutation and precession angular velocities are zero. Find the maximum magnitude of the precession angular velocity ∣ϕ˙∣max|\dot{\phi}|_{\text{max}} (where ϕ\phi is the azimuthal angle around the Z-axis) of the dipole during its subsequent motion. Assume no non-conservative forces are acting on the system.

Options

  • A.

    8pE7I1\sqrt{\frac{8 p E}{7 I_1}}

  • B.

    2pE7I1\sqrt{\frac{2 p E}{7 I_1}}

  • C.

    4pE7I1\sqrt{\frac{4 p E}{7 I_1}}

  • D.

    7pE8I1\sqrt{\frac{7 p E}{8 I_1}}

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Multi-Concept_Bridge

Master problems that require linking physics and math concepts to solve complex competitive questions.

Concepts Behind This Question

Work Done in Rotating Dipole|Gyroscopic Stability|Vector Cross-Product

Why This Question Is Tricky

Common Mistakes

This question tests the advanced application of rigid body dynamics, specifically the gyroscopic motion of a symmetric top in a potential field.

The primary trap lies in assuming the dipole undergoes steady precession (τ⃗=Ω⃗×L⃗\vec{\tau} = \vec{\Omega} \times \vec{L}) from the moment of release, which incorrectly yields ϕ˙=pE/(I3ω3)\dot{\phi} = p E / (I_3 \omega_3) (Option B).

Students often fail to recognize that releasing the dipole from rest (zero initial precession) induces nutation, and the work done by the electric field couples into both the nutational and precessional kinetic energies.

By forcing the use of Euler's equations or Lagrangian conservation laws (EE and LzL_z), the problem discriminates between students who memorize the steady precession formula and those who understand the full dynamical evolution of the angular momentum vector in non-inertial frames.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterElectrostatic Potential and Capacitance - Class 12
ConceptWork Done in Rotating Dipole
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree