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Pointing vectors vec(S) is defined as a vector whose magnitude is equal to the wave intensity and whose direction is along the direction of wave propagation. Mathematically, it is given by vec(S)=(1)/(mu_(0))(vec(E )xx vec(B)). Show the nature of vec(S) vs graph. |
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Answer» Solution :In electromagnetic wave let `vec(E )` is in y - direction `vec(B)` is in z - direction and electromagnetic wave propagate in X - direction energy propagating will be in direction of `vec(E )xx vec(B)` (in x - direction). `vec(E )=E_(0)SIN(OMEGA t-kx)HAT(j)` `vec(B)=B_(0)sin(omega t-kx)hat(k)` `therefore vec(S)=(1)/(mu_(0))(vec(E )xx vec(B))=(1)/(mu_(0))E_(0)B_(0)sin^(2)(omega t-kx)(hat(j)xx hat(k))` `therefore vec(S)=(E_(0)B_(0))/(mu_(0))sin^(2)(omega t-kx)hat(i)[because hat(j)xx hat(k)=hat(i)]` Variation in magnitude of `|vec(S)|` with time is shown in figure shown below. 
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