Practice question

**Field due to infinite plane and shells** illustrates symmetry power. Infinite plane's field remains constant because distant contributions balance, while spherical shell interior field cancels symmetrically, leading to E = 0 inside, E = kQ/r² outside. Outside shell ( r > R ): E = (k q/r²) . k = 9 × 10⁹ N·m²/C² , q = 15 × 10⁻⁶ C , r = 0.3 m . E = 9 × 10⁹ × (15 × 10⁻⁶/(0.3)²) = 9 × 10⁹ × (15 × 10⁻⁶/0.09) = 1.5 × 10⁶ N/C . Substituting values gives 1.5 × 10⁶ N/C, which matches expected magnitude for this electrostatic configuration,