14. The Cartesian coordinates of a charged particle are given by x(t) = 0, y(t) = 0 and z(t) = A cos(ωt). Regarding the electromagnetic (EM) waves it generates, which of the following statement is wrong? (A) At a point on the x-y plane far from the origin, the electric field is polarized in the z direction. (B) At a large distance r, the outgoing EM wave measured at (x, y, z) = (0, 0, r) are stronger than the outgoing EM wave measured at (x, y, z) = (r, 0, 0). (C) The frequency of the EM wave at a generic fixed point in space is ω/(2π). (D) The magnitude of the electric field is approximately proportional to 1/r at large r.

9. In a model gasoline engine, the air-gasoline mixture can be treated approximately with a thermodynamic cycle known as the Otto cycle. In the first process (1→2), the gas undergoes an isentropic compression (the engine's compression stroke), during which the temperature rises from 300 K to 600 K. The next process (2→3) is an isochoric pressure increase, and the gas temperature reaches 1500 K as the gasoline burns. Next (3→4), the gas undergoes isentropic expansion (the engine's power stroke) during which its temperature drops to 800 K. Finally (4→1), the gas experiences an isochoric pressure decrease during which its temperature drops back to 300 K. Please estimate the efficiency of this model engine. (A) 10%~20% (B) 20%~30% (C) 30%~40% (D) 40%~50%.

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