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. The document lists thermopiles, bolometers, and infrared photographic film as detectors for infrared waves. Bolometers are a common choice. Using c = fλ, E₀/B₀ = c, I_d = ε₀ dΦ_E/dt, and spectrum classification λ = c/f, evaluation yields Bolometers, illustrating EM wave transverse nature and Maxwell's displacement current concept.