The magnitude of the Poynting vector of a planar electromagnetic wave has an average value of 0.939 W/m^2 . The wave is incident upon a rectangular area, 1.5 m by 2.0 m, at right angles. How much total electromagnetic energy falls on the area during 1.0 minute?

47 mW

Explanation:

The average value of the Poynting vector, S = 0.939 W/m² = Intensity of wave, I

S = I S

Also, I = P/A where P = Et, P = power of electromagnetic wave, E = energy of electromagnetic wave in time t and t = time = 1 min = 60 s and A = area = lb since the electromagnetic waves falls on area equal to that of a rectangle.

So, S = Et/A

E = SA/t

= Slb/t

= 0.939 W/m² × 1.5 m × 2.0 m/60 s

= 2.817 W/60 s

= 0.047 W

= 47 mW

So, 47 mW of electromagnetic energy falls on the area in 1.0 minute.

the minimum amperage that the current in this wire would have to have so that its weight is completely supported by the magnetic force due to earth's field, assuming that no other forces except gravity act on it

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