The answer is D. Variable. Hope this Helps:)))
The material in which a wave travels is called a medium. Hope this helps!
Answer:
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.
A control is B, standard for comparison. This is used to compare for example plants and using different fertilizers and then have one with no fertilizer. Controls are basically just a base to the entire experiment
I hope this helps you!:)