As a newly-commissioned officer in the US Navy, your team is tasked with updatin

Question

As a newly-commissioned officer in the US Navy, your team is tasked with updating the communication system used by our submarines. Your first step is describe the problem to your superior officers:

1) How deep could submarines operate?

1000 ft

2) If a communication signal reaches the top of the ocean with an intensity of 100Wm2, what is the signal intensity at the depth of the submarine (remember to use ? for saltwater not ?0 )

i think we use the following formula I=(c(1.3*10^-6)(E0)2)/2

Intensity = unit of W/m2, c = 3x10^8 , E0 is the maximum electric field strength. ?value for salt water is about 1.3x10^-6

How do we get E0???

Explanation / Answer

apply Intensity IO = power/area = Emax^2/2uoC

where u0 is constant = 4pi e-7

A = area = pi r^2

and r = D/2 = 1.1/2 = 0.55 mm

C is velocioty of light = 3e8 m/s

so now by substituinon

we get

so Emax^2 = 100 * 2* 4pie-7 * 3e8

Emax = 274.517 N/C

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