(a) What is a standing wave? Describe reasons for causing it. (b) A 200- MHz uniform plane wave is traveling in free space in the positive z direction. At z=0, the wave strikes normal to the surface a large block of material having ϵ r =4, μ r =9,σ=5 S/m. If the incident magnetic field intensity vector is given by H i (z,t)=cos(ωt−β o​ z)a yA/m (i) Write complete time-domain expressions for the incident, reflected, and transmitted electric field vectors. (ii) Determine the time-average power density associated with the transmitted wave.