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Question #42007

Difficulty: 8/10 | 🟢 Free

The Question

A point charge +Q+Q is fixed at the origin of a coordinate system. A small planar sensor of area AA is constrained to move along the curve y=x3y = x^3 (where x>0x > 0) in the xyxy-plane. The sensor's surface normal n^\hat{n} is mechanically maintained parallel to the positive yy-axis (n^=j^\hat{n} = \hat{j}). The magnitude of the electric field EE at the sensor's location is determined experimentally by measuring the electric flux ΔΦ\Delta \Phi through the sensor, its area AA, and its xx-coordinate. During an experiment at x=1 mx = 1 \text{ m}, the relative error in measuring the flux is 1.5%1.5\%, and the relative error in measuring the area is 1.0%1.0\%. The absolute error in measuring the xx-coordinate is 0.02 m0.02 \text{ m}. Assuming the errors are independent and add up to give the maximum possible error, what is the maximum percentage relative error in the calculated value of the electric field EE?

Options

  • A.

    2.5%2.5\%

  • B.

    4.5%4.5\%

  • C.

    8.5%8.5\%

  • D.

    10.5%10.5\%

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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

Flux and Surface Geometry|Relative Error Propagation in Powers

Why This Question Is Tricky

Common Mistakes

This question tests the rigorous application of Gauss's Law and error propagation by breaking the standard assumption of a spherical Gaussian surface.

Students often memorize the relative error formula ΔE/E=ΔΦ/Φ+ΔA/A\Delta E/E = \Delta \Phi/\Phi + \Delta A/A and ignore the geometric coupling between the field vector and the surface normal.

By constraining the sensor to a non-spherical curve (y=x3y=x^3) with a fixed normal orientation, the effective area becomes a complex function of the coordinates.

The lethal trap is failing to account for the angular dependency (cos⁡θ\cos\theta) in the flux equation, which introduces a non-linear error propagation term from the xx-coordinate measurement.

Students who ignore the angle calculate 2.5%2.5\%, while those who incorrectly assume E∝1/r2E \propto 1/r^2 without resolving the dot product calculate 10.5%10.5\%.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterUnits and Measurements - Class 11 Part 1
ConceptRelative Error Propagation in Powers
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree