Superconductivity characterized by: MCQ with Answer and Explanation

Explanation:
Thermal expansion. Rails expand in summer heat, gap prevents buckling. Linear expansion ΔL = α L ΔT.

Explanation:
B ∝ N. Double turns ⇒ double field at center. Direct proportionality from Biot-Savart law. Memory tip: 'Coil field: B ∝ NI; more turns ⇒ stronger field'. Magnetism formula frequently tested in competitive exams.

Explanation:
Dispersion: n varies with λ (Cauchy's law), causing different refraction angles for colors. Frequency constant across media; wavelength changes. Memory aid: 'n(λ) ⇒ v(λ) ⇒ different bending; violet bends most'. Conceptual question testing dispersion mechanism, frequently examined in competitive optics sections.