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Question #42437
The Question
A uniform conducting rod of mass and length rests symmetrically on two parallel, rough horizontal rails separated by a distance . The rails are parallel to the y-axis and the rod is parallel to the x-axis. A uniform magnetic field exists in the region, where . The coefficient of static friction between the rod and the rails is . If a current is passed through the rod in the direction, what is the minimum current required to just initiate sliding of the rod? (Take )
Options
- A.
- B.
- C.
- D.
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
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 ().
By failing to recognize that the vertical magnetic force reduces the normal force, students incorrectly assume , 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
| Subject | Physics |
| Chapter | Laws of Motion - Class 11 Part 1 |
| Concept | Static Friction Threshold |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |