QuestionElectromagnetic waves
An electromagnetic wave with its magnetic field \(\mathbf{B} = 0.3\cos(ky - 10^8 t)\hat{i}\) tesla is propagating in a non-magnetic dielectric medium of refractive index 2. The wavelength of the wave is
- (a) 6π m
- (b) 3π m
- (c) 0·3 m
- (d) (2π/3) m
Answer: (b) 3π m
From the wave, ω = 10⁸ rad s⁻¹. Speed in medium v = c/n = 3×10⁸/2 = 1·5×10⁸ m s⁻¹. Wave number k = ω/v = 10⁸/1·5×10⁸ = 2/3 m⁻¹. Wavelength λ = 2π/k = 2π × 3/2 = 3π m → (b).