6. A radio station broadcasts electromagnetic waves with a power of 2000 W. Assume the station acts as a point source. What is the amplitude of the electric field at a position 860-m away from the station? (A) 0.8 V/m (B) 0.7 V/m (C) 0.6 V/m (D) 0.5 V/m (E) 0.4 V/m

5. In general, the resistivity of a conductor increases as the temperature increases. However, the resistivity of a pure semiconductor may decreases as the temperature increases. What is the possible reason of this unusual behavior of semiconductor? (A) The collisions between free electrons and atoms are reduced as the temperature increases. (B) The collisions between free electrons and atoms are enhanced as the temperature increases. (C) The drift velocity of electrons is increased as the temperature increases. (D) The electron density is decreased as the temperature increases. (E) The electron density is increased as the temperature increases.

6. A radio station broadcasts electromagnetic waves with a power of 2000 W. Assume the station acts as a point source. What is the amplitude of the electric field at a position 860-m away from the station?
(A) 0.8 V/m
(B) 0.7 V/m
(C) 0.6 V/m
(D) 0.5 V/m
(E) 0.4 V/m

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