Lens power P = -4 D. Focal length and type: MCQ with Answer and Explanation

Explanation:
Fuse uses heating effect (Joule heating I²R). When current exceeds limit, fuse wire melts due to heat, breaking circuit. Motor uses magnetic effect, generator uses electromagnetic induction, galvanometer detects current. Iron box, heater also use heating effect.

Explanation:
nano = 10⁻⁹. So 1 nm = 10⁻⁹ m. Angstrom = 10⁻¹⁰ m. picometer = 10⁻¹² m.

Explanation:
Using Gauss's law, for an infinite sheet, electric field E = σ/(2ε₀), directed perpendicular to the sheet. This is uniform and independent of distance from the sheet. Option A is for field near conductor surface; C and D are incorrect. Memory aid: 'Infinite sheet: E = σ/(2ε₀); conductor surface: E = σ/ε₀'. This conceptual question tests electrostatics fundamentals, crucial for competitive exams. Always distinguish between conducting and non-conacting sheets, as field expressions differ due to charge distribution.