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Question #77831

Difficulty: 8/10 | 🟢 Free

The Question

A non-uniform electric field is given by E⃗=E0(1+αz)k^\vec{E} = E_0 (1 + \alpha z) \hat{k}, where E0E_0 is an unknown constant and α=2.0 m−1\alpha = 2.0 \text{ m}^{-1} is a known exact constant. A student determines E0E_0 by measuring the electric flux Φ\Phi through an open surface SS bounded by the curve x2+y2=R2x^2+y^2=R^2 in the xyxy-plane. The true surface SS is a paraboloid defined by z=R−x2+y2Rz = R - \frac{x^2+y^2}{R} for z≥0z \ge 0. The student measures the base radius as R=1.0 mR = 1.0 \text{ m} with a relative error eR=ΔRRe_R = \frac{\Delta R}{R}, and the flux Φ\Phi with a relative error eΦe_\Phi. However, the student incorrectly assumes the surface SS is a standard hemisphere of radius RR (z=R2−x2−y2z = \sqrt{R^2 - x^2 - y^2}). Let etruee_{true} be the true maximum relative error in E0E_0 (derived from the correct surface geometry), and estudente_{student} be the maximum relative error calculated by the student using their flawed geometric assumption. What is the magnitude of the difference ∣estudent−etrue∣|e_{student} - e_{true}|? (Assume the normal to the surface has a positive z-component).

Options

  • A.

    114eR\frac{1}{14} e_R

  • B.

    314eR\frac{3}{14} e_R

  • C.

    17eR\frac{1}{7} e_R

  • D.

    514eR\frac{5}{14} e_R

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

Flux and Surface Geometry|Relative Error Propagation in Powers

Why This Question Is Tricky

Examiner Levers

Negative Thinking

Uses "NOT", "EXCEPT", or "INCORRECT" to flip the logic gate.

Difficulty Boost : +2

Visualization Stress

Requires mental rotation or 3D mapping (Optics/Geometry/Vectors).

Difficulty Boost : +4

Common Mistakes

This question tests the rigorous application of error propagation derived from first-principles vector calculus, weaponizing the definition of electric flux.

Students typically memorize the relative error formula for flux as ΔE/E=ΔΦ/Φ+2ΔR/R\Delta E/E = \Delta \Phi/\Phi + 2\Delta R/R, assuming a standard uniform field and spherical surface.

By introducing a non-spherical, variable-curvature surface (paraboloid) and a field with a spatial gradient (αz\alpha z), the effective area becomes a complex polynomial function of the coordinates.

The lethal collision occurs when the student ignores that the 'power' of the radius in the error formula changes based on the flux penetration angle and the specific geometry of the surface.

The error propagates non-linearly through the spatial dependency of the flux, rendering the standard Power Law rule mathematically insufficient and exposing the flaw in assuming a generic hemispherical geometry.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterUnits and Measurements - Class 11 Part 1
ConceptRelative Error Propagation in Powers
Difficulty8
Cognitive Load8
Target Solve Time180 sec
AccessFree