Question

The intensity of electromagnetic wave at a distance of 1km from a source of power 12.56 kw is
(A) 10-3 Wm-2
(B) 4x10-3Wm-2
(C) 12.56x10-3Wm-2
(D) 1.256x10-3Wm-2​

Answer 1

Answer:

I thing your answere

Explanation:

option (A)

Answer 2

Answer:

The intensity of electromagnetic wave at a distance of 1km is $10^{-3} Wm^{-2}$

Explanation:

Given the distance of a point from the source,  $r=1km=10^{3} m$

        and power emitted by the source,  $P=12.56 kW=12.56 \times 10^{3} W$

Intensity(I) is defined as the power emitted per unit area, given by

                          $I=\frac{P}{4\pi r^{2} }$

                             $=\frac{12.56\times 10^{3} }{4\times 3.14 \times (10^{3}) ^{2} }$

                             $= 10^{-3} W/m^{2}$

Hence, the intensity of electromagnetic wave is $10^{-3} W/m^{2}$

The correct answer is option A.