How much energy is transported by an EM wave with a given E field strength?

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Homework Help Overview

The discussion revolves around calculating the energy transported by an electromagnetic (EM) wave with a specified electric field strength. The original poster is working with an rms electric field strength of 36.5 mV/m and an area of 1.15 cm², seeking to determine the energy transported per hour.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the relationship between electric field strength and energy density, referencing relevant equations and unit conversions. There is an exploration of the correct application of formulas and unit consistency, particularly regarding area conversion and the calculation of energy transported over time.

Discussion Status

The conversation includes attempts to clarify the calculations involved, with one participant confirming the conversion of area to square meters. There is also acknowledgment of potential errors in the calculations and conceptual understanding, with participants providing guidance on unit handling and formula application.

Contextual Notes

Participants are working under the constraints of homework guidelines, which may limit the sharing of complete solutions. There is an emphasis on understanding the underlying physics concepts and ensuring correct unit conversions throughout the problem-solving process.

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Homework Statement


How much energy is transported across a 1.15 cm^2 area per hour by an EM wave whose E field has an rms strength of 36.5 mV/m?

Homework Equations



E=hv?
The big problem I'm having is that I don't know what formulae to use.

The Attempt at a Solution


I know what V/m = J/C = J/(A*s) and I know I need to get to J/h. But I don't know what I have that would include Amps or Coloumbs to get rid of that part (I've resorted to trying to sort out units in the face of the lack of equations.

Thanks!
 
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Queue said:

Homework Statement


How much energy is transported across a 1.15 cm^2 area per hour by an EM wave whose E field has an rms strength of 36.5 mV/m?

Homework Equations



E=hv?
The big problem I'm having is that I don't know what formulae to use.

The Attempt at a Solution


I know what V/m = J/C = J/(A*s) and I know I need to get to J/h. But I don't know what I have that would include Amps or Coloumbs to get rid of that part (I've resorted to trying to sort out units in the face of the lack of equations.

Thanks!

Ok, I have from my book (which was just returned to me) that energy in a wave is given by \epsilon_0 E2 with units of J/m3. So I have u = 8.85*10-12*(36.5*10-3)2. From there I divided by the area I am given (1.15 cm2) and then multiplied by the speed of light (in hours) to give me the right units but my answer was incorrect according to mastering physics. Perhaps I made a math error or perhaps I'm having conceptual issue. Any help would be appreciated.
 
I think you did it correctly, but I'll just ask if you converted the area to m2 units
 
I did convert to square meters.

I multiplied by area, didn't divide like I thought I was supposed to which actually makes my units work out.

This gives me u = [tex]\epsilon_0 E^2[/tex] = 8.85*10-12*(3.65*103)2 J/(m3). From there I have u*A = 8.85*10-12*(3.65*103)2*0.000115 J/m. Then I multiplied by c giving u*A*c = 8.85*10-12*(3.65*103)2*0.000115*3*109 = whatever it is J/s. Then I just multiplied by 3600 (seconds per hour) to get J/h.

Thanks!
 
Last edited:

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