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Question #42304

Difficulty: 8/10 | 🟢 Free

The Question

An electric dipole of dipole moment magnitude pp is initially placed at the origin OO of a coordinate system, pointing in the +y+y-direction. It is immersed in a non-uniform electrostatic field given by E⃗=α(xi^−yj^)\vec{E} = \alpha (x \hat{i} - y \hat{j}), where α\alpha is a positive constant. The dipole is moved to the point A(d,d)A(d, d) and rotated to point in the +x+x-direction. Consider two distinct processes for this transition:

Process 1: The dipole is first translated from OO to AA along the line y=xy=x while maintaining its orientation in the +y+y-direction. Then, at point AA, it is rotated in the xyxy-plane to align with the +x+x-direction. Process 2: The dipole is first rotated at OO in the xyxy-plane to align with the +x+x-direction. Then, it is translated from OO to AA along the line y=xy=x while maintaining this new orientation.

Let WT1W_{T1} and WR1W_{R1} be the translational and rotational work done by the electric field in Process 1, respectively. Let WT2W_{T2} and WR2W_{R2} be the corresponding works in Process 2. Which of the following options correctly gives these quantities?

Options

  • A.

    WT1=−pαd,  WR1=2pαd,  WT2=pαd,  WR2=0W_{T1} = -p \alpha d, \; W_{R1} = 2p \alpha d, \; W_{T2} = p \alpha d, \; W_{R2} = 0

  • B.

    WT1=0,  WR1=pαd,  WT2=pαd,  WR2=0W_{T1} = 0, \; W_{R1} = p \alpha d, \; W_{T2} = p \alpha d, \; W_{R2} = 0

  • C.

    WT1=−pαd,  WR1=pαd,  WT2=0,  WR2=pαdW_{T1} = -p \alpha d, \; W_{R1} = p \alpha d, \; W_{T2} = 0, \; W_{R2} = p \alpha d

  • D.

    WT1=pαd,  WR1=0,  WT2=−pαd,  WR2=2pαdW_{T1} = p \alpha d, \; W_{R1} = 0, \; W_{T2} = -p \alpha d, \; W_{R2} = 2p \alpha d

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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

Dot Product Geometry|Dipole Potential Angular Dependence|Integration

Why This Question Is Tricky

Common Mistakes

This question targets the misconception that translational and rotational work done on a dipole are state functions like potential energy.

While the total work W=−ΔUW = -\Delta U is path-independent in a conservative field, the individual contributions Wtrans=∫(p⃗⋅∇)E⃗⋅dr⃗W_{trans} = \int (\vec{p} \cdot \nabla)\vec{E} \cdot d\vec{r} and Wrot=∫(p⃗×E⃗)⋅dθ⃗W_{rot} = \int (\vec{p} \times \vec{E}) \cdot d\vec{\theta} are highly path-dependent.

Students who blindly apply W=−ΔUW = -\Delta U without integrating the spatial gradient of the field (force) and the angular dependence (torque) separately will fail to find the correct individual components, exposing a critical gap in understanding the Work-Energy Theorem for extended bodies in non-uniform fields.

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Question Information

SubjectPhysics
ChapterWork, Energy, and Power - Class 11 Part 1
ConceptDot Product Geometry
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree