4.A uniform plane wave is traveling in free space with the electric field intensity: = 12 cos(ωt + 5z) , where ω is the frequency, k is a constant, and is the unit vector in x direction. What is the propagation velocity of the wave?(A) 3×10⁸ m/s (B) 1.8×10⁹ m/s (C) -3×10⁸ m/s (D) -1.8×10⁹ ẑ m/s (E) -1.8×10⁹ m/s

1.In the figure shown on the right, a wire is extended from y = -(a+L) to y = a+L and is bent as a semicircle in the xy plane. If the wire carries a current I flowing along the direction indicated by the arrows and the magnetic flux density B in the region is along the +z direction, determine the magnetic force acting on the semicircular arc with the following parameters: I = 2 A, B = 5 T, a = 1 m, L = 2 m. (A) 10 Nt (B) 20 Nt (C) 30 Nt (D) 40 Nt (E) 5 Nt

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