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The Second Law of Thermodynamics states that for an isolated system, entropy always increases or remains constant, never decreases. This defines the direction of spontaneous processes and the arrow of time.

Using lens formula: 1/f = 1/u + 1/v. Given f = 15 cm, v = 30 cm: 1/15 = 1/u + 1/30, so 1/u = 1/15 - 1/30 = 1/30, therefore u = 30 cm.

Linear expansion: ΔL = α × L₀ × ΔT = 1.2 × 10⁻⁵ × 1 × 100 = 1.2 × 10⁻³ m = 1.2 mm.

Work done against constant pressure: W = -PΔV. Given W = -500 J and P = 2 atm = 2 × 101325 Pa. ΔV = -W/P = 500/(2 × 101325) ≈ 2.47 × 10⁻³ m³ = 2.47 L.

De Broglie proposed that all matter exhibits wave-particle duality. Both light (photons) and electrons show properties of both waves and particles, confirmed by experiments like double-slit interference and photoelectric effect.

Ferromagnetism is the property of materials like iron, cobalt, and nickel to retain permanent magnetic properties due to aligned electron spins.

For parallel connection: 1/R = 1/6 + 1/3 + 1/2 = 1/6 + 2/6 + 3/6 = 6/6 = 1. Therefore R = 1Ω.

Work by gravity W = -mgh (negative because displacement is opposite to force direction). W = -5 × 10 × 10 = -500 J.

Insulin, produced by the pancreas, lowers blood glucose by facilitating glucose uptake into cells. Glucagon raises blood glucose levels.

Elastic potential energy U = ½kx². U = ½ × 100 × (0.2)² = 50 × 0.04 = 2 J.