Converting Watts, Distributed Over An Area, To Energy Density

In summary: I'm sorry, I'm not following. You said power flux through volume doesn't make sense. Then, power flux through a surface section does. What's the difference?Power flux through a surface section is just a more localized version of power flux through volume. It doesn't involve the entire area. Just a small subsection of it.
  • #1
jaketodd
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Is there a way to get energy density from watts, with the resultant energy density not involving time, as watts do?

Thanks,

Jake
 
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  • #2
You have not supplied enough information.

First of all energy density is not well defined in your question. Depending on the context it could mean energy per unit volume or energy per unit mass. You stated that you are starting with power per unit area so (J/t)/m2 or J/tm2. Assuming that by energy density you mean energy per unit volume the units are J/m3 so in order to equate the 2 you need to be able to equate time to meters. In other words, you need the velocity of the energy.
 
  • #3
jaketodd said:
Is there a way to get energy density from watts, with the resultant energy density not involving time, as watts do?

Thanks,

Jake

Watt is a unit of power, and is equal to a joule per second. If you have a power and want to know an energy density, you need to multiply the power by some interval of time and divide by the area or volume to which the power is distributed.
 
  • #4
Thanks guys...

The watts travel at the speed of light. Also, the volume is m[itex]^{3}[/itex]. Does this help get an answer?

Thanks,

Jake
 
  • #5
I'm looking for a conversion of watts, given that they travel at the speed of light, over a predefined area, which I could, perhaps, multiply by. In other words, I'm trying to get the energy density.

Thanks,

Jake
 
  • #6
So you have either RF radiation or some other massless boson field flux through a given area. Easy.

[tex]\rho_E = \frac{P}{A c}[/tex]

Edit: Note that it gives you J/m³, which is what you want, if I'm not mistaken.
 
  • #7
K^2 said:
So you have either RF radiation or some other massless boson field flux through a given area. Easy.

[tex]\rho_E = \frac{P}{A c}[/tex]

Edit: Note that it gives you J/m³, which is what you want, if I'm not mistaken.

Excellent. However, I think I shot myself in the foot by saying "area." I meant volume. I assume the 'A' in your equation is for two-dimensional area, and not volume? And, yes, [itex]\stackrel{J}{m^{3}}[/itex] is what I want.

EDIT: Actually I think what you gave me might work for my purposes, but it would be nice to have answered this latest query.

Thanks!

Jake
 
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  • #8
Power flux through volume doesn't make sense. Power flux through a give surface section does. That's what you need to know to find the average energy density of whatever's flowing past.

Think about it in terms of analogous situation with electrical current. The quantities correspond as follows.

[tex]P \rightarrow I[/tex]
[tex]A \rightarrow A[/tex]
[tex]\rho_E \rightarrow \rho_q[/tex]
[tex]c \rightarrow v[/tex]

Where v is drift velocity, and I is total current flowing through cross section. Then you know that current is given by this expression.

[tex]I = \rho_q A v[/tex]

Rearrange the terms, and you get the same thing.
 
  • #9
Like I said in the edit, I think what you have provided will suffice for me, and I thank you greatly!

Jake
 

FAQ: Converting Watts, Distributed Over An Area, To Energy Density

What is the formula for converting watts to energy density?

The formula for converting watts to energy density is: Energy Density = Power / Area.

How do I convert watts per square meter to energy density?

To convert watts per square meter to energy density, simply divide the power by the area.

Can energy density be negative?

No, energy density cannot be negative. It is a measure of the amount of energy present in a given area, and energy cannot have a negative value.

What are the common units of measurement for energy density?

The common units of measurement for energy density are joules per square meter (J/m2) and watt-hours per square meter (Wh/m2).

Why is energy density an important concept in science?

Energy density is an important concept in science because it allows us to compare the amount of energy present in different areas. It is also useful in understanding the efficiency of energy sources and their impact on the environment.

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