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Question #42843

Difficulty: 8/10 | 🟢 Free

The Question

In a region of space, two independent static electric potentials are established, given by: V1(x,y,z)=E0xexp⁡(−z2R2)V_1(x,y,z) = E_0 x \exp\left(-\frac{z^2}{R^2}\right) V2(x,y,z)=E0yexp⁡(−z2R2)V_2(x,y,z) = E_0 y \exp\left(-\frac{z^2}{R^2}\right) where E0E_0 is a positive constant with units of V/m\text{V/m}, and RR is a positive constant with units of meters. The corresponding electric fields are E⃗1=−∇V1\vec{E}_1 = -\nabla V_1 and E⃗2=−∇V2\vec{E}_2 = -\nabla V_2. A new vector field is defined as G⃗=E⃗1×E⃗2\vec{G} = \vec{E}_1 \times \vec{E}_2. What is the magnitude of the flux of G⃗\vec{G} through the open hemispherical surface defined by x2+y2+z2=R2x^2 + y^2 + z^2 = R^2 with z≥0z \ge 0?

Options

  • A.

    πR2E02\pi R^2 E_0^2

  • B.

    πR2E02e\frac{\pi R^2 E_0^2}{e}

  • C.

    0

  • D.

    2πR2E022\pi R^2 E_0^2

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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|Conservative Field Path Independence|Gradient Operator

Why This Question Is Tricky

Common Mistakes

This problem tests the student's ability to recognize that the cross product of two conservative fields (electrostatic fields) has zero divergence.

The primary trap is attempting a 'brute force' surface integration of the vector field G⃗\vec{G} over the hemispherical surface.

Due to the Gaussian exponential term, this integral appears analytically intractable, causing students to either guess zero or waste significant time.

By applying Gauss's Divergence Theorem (or alternatively, Stokes' Theorem), the student can bypass the complex geometry and evaluate the flux over the flat circular base, where the fields simplify to uniform vectors.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterElectric Charges and Fields - Class 12
ConceptFlux and Surface Geometry
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree