Practice question

**Aerials produce radio waves** by rapid acceleration/deceleration of electrons in antenna driven by AC, frequency equals driving frequency, for 60 MHz, λ=c/f=3×10⁸/60×10⁶=5 m, half-wave antenna length λ/2=2.5 m, efficient radiation when antenna size comparable to λ. c = (1/√(μ₀ ε₀)) . Substituting values, μ₀ ε₀ = (4 π × 10⁻⁷) × (8.85 × 10⁻¹²) ≈ 1.11 × 10⁻¹⁷ . Thus, c = (1/√(1.11 × 10⁻¹⁷)) ≈ 3 × 10⁸ m/s . Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ = c/f, evaluation yields 3 × 10⁸ m/s, illustrating EM wave transverse nature and Maxwell's displacement current concept.