Physics 21 Fall 2007 Solution to HW-24 Poynting Flux An electromagnetic wave travels through vacuum. Its electric field vector is given by E =E_0 sin( k x-ϖ t ) j . (A) If B_0 is the amplitude of the magnetic field vector, find the complete expression for the magnetic field vector B of the wave. B_0 sin( kx-ϖ t ) k (B) What is the Poynting vector S ( x,t ) (the power per unit area associated with the electromagnetic wave ? Satellite Television Transmission A satellite is in geostationary orbit at a height of 35,000 km above the surface of the earth and has an isotropic power output of 1 kW. (A) Reception devices pick up the electromagnetic wave sent out by the satellite. What is the amplitude E_0 of the electric field vector of the satellite broadcast as measured at the surface of the earth? (B) Suppose the satellite transmits television signals. You have a satellite TV reciever with a circular dish of radius R that focuses the electromagnetic energy incident from the satellite onto a receiver with a surface area of 5
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