Poynting vector and luminosity

In summary: Overall, the Poynting vector is an important tool in describing and understanding electromagnetic fields, particularly in the context of radiation from point sources. In summary, the Poynting vector is a vector quantity that describes the rate of energy flow in an electromagnetic field, and can be used to calculate the incident intensity of radiation on a curved surface from a point source.
  • #1
mikeph
1,235
18
Hello

Say I have a source of radiation placed at my origin and I know its power is spread uniformly about 2*pi at a certain frequency, I believe this is also called luminosity. (or a 2D equivalent)

This means if I put a shell around the source and collect this power, then as long as the shell is closed and contains the origin, I collect all my power back - implying there is some vector field which is subject to the divergence theorem - is this the Poynting vector?

I want to know what this field is for a point source, and get to grips with the working of the vector field, because ultimately I am planning to find the incident intensity over a complicated curved surface (I am hoping to integrate the dot product of this field with my normal to the surface).I hope this make sense and I haven't asked a question without giving enough information because I am a little hazy on Poynting vectors.
Thanks
 
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  • #2
Yes, the Poynting vector can be used to describe the radiation field from a point source. The Poynting vector is a vector quantity that describes the rate of energy flow in an electromagnetic field, and is given by the equationS = E × Bwhere E is the electric field intensity and B is the magnetic field intensity. In your case, the Poynting vector will be a function of the power from your source, the frequency of the radiation, and the distance from the source. You can use this to calculate the intensity of the radiation incident on a curved surface by integrating the dot product of the Poynting vector with the surface normal.
 

1. What is the Poynting vector?

The Poynting vector is a mathematical quantity used to describe the flow of electromagnetic energy. It is a vector quantity, meaning it has both magnitude and direction, and is defined as the cross product of the electric field and magnetic field vectors.

2. How is the Poynting vector related to luminosity?

The Poynting vector is directly related to luminosity, which is the total amount of electromagnetic energy emitted by an object per unit time. The Poynting vector represents the flow of this energy, and its magnitude is proportional to the luminosity of the source.

3. How is the Poynting vector used in physics?

The Poynting vector is used in many areas of physics, including electromagnetism, optics, and energy transfer. It is a fundamental quantity in Maxwell's equations, which describe the behavior of electric and magnetic fields, and it is also used to calculate the energy flux in electromagnetic waves.

4. What is the significance of the direction of the Poynting vector?

The direction of the Poynting vector is important as it indicates the direction of energy flow. In electromagnetic waves, the Poynting vector points in the direction of propagation, showing that electromagnetic energy is traveling in that direction. In other cases, such as in the presence of a magnetic field, the direction of the Poynting vector can reveal information about the forces acting on charged particles.

5. Can the Poynting vector be negative?

Yes, the Poynting vector can have a negative value. This indicates that the energy is flowing in the opposite direction of the vector's direction. In electromagnetic waves, this can occur when the wave is reflected or when the electric and magnetic fields are out of phase with each other.

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