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A plane electromagnetic wave in free space is specified by the electric field
E = ax [20 cos (ωt – βz) + 5 cos (ωt + βz)] V/m.
The associated magnetic field is—
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ay [20 cos (ωt + βz) + 5 cos (ωt + βz)] A/m ∏ -
ay [20 cos (ωt + βz) − 5 cos (ωt + βz)] A/m ∏ -
ay [20 cos (ωt − βz) + 5 cos (ωt + βz)] A/m 120∏ -
ay [20 cos (ωt − βz) − 5 cos (ωt + βz)] A/m 120∏
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Correct Option: C
E and H are related by η
i.e. E/ H = η,
the characteristic impedance of the medium which is 120 π for free space. Also, phase of H in the reflected component of the wave has to reverse so that travelling of the reflected wave is correctly given by the direction of E × H.
Of course, E × H are perpendicular to each other in the incident component or the forward travelling component of the wave. Keeping in view the above facts and the given expression for E.
H = ay (1/ 120 π) 20 cos (ωt – βz) – 5 cos (ωt + βz) A /m.
