Start Learning Free

Before You Begin

Question #42933

Difficulty: 8/10 | 🟢 Free

The Question

A solid non-conducting sphere of radius RR (in meters) has a uniform volume charge density ρ\rho (in C/m3\text{C/m}^3). The sphere is centered at the origin (0,0,0)(0,0,0) of a Cartesian coordinate system. A spherical cavity of radius R/2R/2 is created inside the sphere, with its center located at (R/2,0,0)(R/2, 0, 0). The entire setup is placed in an external electric field given by E⃗ext=−ρε0(xi^−y2j^−z2k^) V/m\vec{E}_{ext} = -\frac{\rho}{\varepsilon_0} \left( x \hat{i} - \frac{y}{2} \hat{j} - \frac{z}{2} \hat{k} \right) \text{ V/m}, where x,y,x, y, and zz are the coordinates in meters. Find the coordinates (x,y,z)(x, y, z) of the neutral point (the point where the net electric field is zero) inside the cavity. Assume the permittivity of free space is ε0\varepsilon_0.

Options

  • A.

    (R6,0,0) m\left( \frac{R}{6}, 0, 0 \right) \text{ m}

  • B.

    (0,0,0) m\left( 0, 0, 0 \right) \text{ m}

  • C.

    (R2,0,0) m\left( \frac{R}{2}, 0, 0 \right) \text{ m}

  • D.

    (−R6,0,0) m\left( -\frac{R}{6}, 0, 0 \right) \text{ m}

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Intuition_Breaker

Train your brain to resist "obvious" answers that are designed to deceive your intuition.

Concepts Behind This Question

Non-conducting Charged Sphere|Neutral Equilibrium Points|Cavity Field Shielding

Why This Question Is Tricky

Common Mistakes

This question tests the student's ability to distinguish between the electrostatic properties of conducting and non-conducting materials with cavities.

A common lethal mistake (the 'shielding trap') is assuming that the electric field inside any cavity is zero, misapplying the Faraday cage effect of conductors to a non-conducting charge distribution.

If a student falls for this trap, they will incorrectly assume E⃗cavity=0\vec{E}_{cavity} = 0 and solve only for E⃗ext=0\vec{E}_{ext} = 0, leading to the origin (0,0,0)(0,0,0).

Furthermore, it rigorously tests the superposition principle and vector addition of fields, ensuring students can handle 3D coordinate geometry alongside Gauss's Law.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterElectric Charges and Fields - Class 12
ConceptNon-conducting Charged Sphere
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree