Question

The magnetic field, (in tesla) in a plane EM wave, propagating along the x–axis, is given by

B = B_y = 3 x 10^-8 sin(10³ x - 3 x 10¹¹ t)

The frequency of the EM wave, and the part of the EM spectrum, to which this wave could belong, are given, respectively, by

(1) 23.9 GHz; (short radio waves / microwaves)

(2) 23.9 GHz; (infrared waves)

(3) 47.7 GHz; (infrared waves)

(4) 47.7 GHz; (short radio waves / microwaves)

Answer 1

(4) 47.7 GHz; (short radio waves / microwaves)

Comparing the given equation with its standard form, namely, B_y = B₀ sin(kx - ωt), we find that 

This frequency corresponds to the (short radio wave / microwave) part of the EM spectrum. (The infrared waves have frequencies of the order of 10¹² Hz to 10¹⁴ Hz).