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Question #42437

Difficulty: 8/10 | 🟢 Free

The Question

A uniform conducting rod of mass m=0.14 kgm = 0.14 \text{ kg} and length L=0.5 mL = 0.5 \text{ m} rests symmetrically on two parallel, rough horizontal rails separated by a distance LL. The rails are parallel to the y-axis and the rod is parallel to the x-axis. A uniform magnetic field B⃗=B0(3i^+4j^+5k^)\vec{B} = B_0 (3\hat{i} + 4\hat{j} + 5\hat{k}) exists in the region, where B0=0.1 TB_0 = 0.1 \text{ T}. The coefficient of static friction between the rod and the rails is μ=0.5\mu = 0.5. If a current II is passed through the rod in the +x+x direction, what is the minimum current II required to just initiate sliding of the rod? (Take g=10 m/s2g = 10 \text{ m/s}^2)

Options

  • A.

    2.0 A2.0 \text{ A}

  • B.

    2.8 A2.8 \text{ A}

  • C.

    3.5 A3.5 \text{ A}

  • D.

    4.7 A4.7 \text{ A}

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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

Static Friction Threshold|Lorentz Force Vector Direction|Newton’s Third Law Pairing

Why This Question Is Tricky

Common Mistakes

This question tests the coupling of 3D Lorentz forces with rigid body mechanics, specifically targeting the dynamic modulation of the normal force.

A common trap for students is to either compute the magnitude of the entire magnetic force and equate it to friction, or to ignore the vertical component of the cross-product (i^×j^=k^\hat{i} \times \hat{j} = \hat{k}).

By failing to recognize that the vertical magnetic force reduces the normal force, students incorrectly assume N=mgN = mg, leading to an overestimation of the required current (Option B).

Another trap is reversing the cross-product order, which incorrectly adds to the normal force (Option D).

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterLaws of Motion - Class 11 Part 1
ConceptStatic Friction Threshold
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree