Question

Four students made the following statements about the propagation of EM waves via the ground wave mode

(A) The waves glide over the surface of the earth and lose energy because of the currents, induced by them, in the ground. 

(B) This mode is useful for transmission of EM waves of frequencies more than 40 MHz, the range of coverage gets limited due to the curvature of the earth. 

(C) The waves propagate throgh air, this mode is useful only for EM waves of frequencies less than a few MHz. 

(D) The wves glide over the surface of the earth; they lose energy primarily because of the energy absorbed by the intervening air. The correct statement is that of student.

(1) A

(2) B

(3) C

(4) D

Answer 1

(1) A

In the ground wave mode of propagation, the wave glides over the surface of the earth. It induces currents in the ground over which it passes and this results in its loss of energy. This mode is practicable only for frequencies less than a few MHz.