Poynting Theorem is one of the key topics that we study under EM wave propagation. And, related to the Poynting Theorem or energy propagation we come across with Poynting Vector. Some people call this as Pointing Vector. So what is correct, Poynting or Pointing? Let’s see.

You can watch the quick video below or read along.

## Power of EM wave and Poynting Theorem

The Poynting theorem, named after the physicist John Henry Poynting, is a fundamental principle in electromagnetism that describes the flow of energy in an electromagnetic field.

Poynting theorem states that the total power flowing through a given surface is equal to the rate of decrease of the electromagnetic energy density within that volume plus the ohmic power loss in that volume.

-\oint_s\left(\overrightarrow E\times\overrightarrow H\right)\cdot\overrightarrow{ds}=\frac\partial{\partial t}\int_v\left[\frac12\varepsilon E^2+\frac12\mu H^2\right]dv+\int_v\sigma E^2dv### Poynting Vector

The Poynting vector describes the direction and magnitude of the flow of electromagnetic energy.

\overrightarrow P=\overrightarrow E\times\overrightarrow Hwhere E is the electric field and H is the magnetic field.

The direction of the Poynting vector is perpendicular to both E and H, and its magnitude is proportional to the product of their magnitudes.

#### Now let’s come back to our question, Poynting or Pointing?

We can conclude that the term \overrightarrow P=\overrightarrow E\times\overrightarrow H is analogous to the power of uniform plane wave the power carried out by the EM wave.

And this analytical treatment was first time done by English physicist John H. Poynting and hence Poynting theorem.

Poynting it is the name of scientist.

And vector \overrightarrow P=\overrightarrow E\times\overrightarrow Hmust be called as **Poynting Vector**.

But, do you know that even if you write this as **Pointing Vector**; then also no problem! Then also you are correct, no problem!

You can also write it as the Pointing vector, why the reason is very simple!

The direction of that propagation of power the direction of the propagation of that energy; it is given by the direction of \overrightarrow P=\overrightarrow E\times\overrightarrow H.

E cross H points towards the direction of propagation.

What is direction of propagation?

It is the direction where power is flowing; along which the energy is flowing.

So basically E cross H is pointing along the direction of propagation.

So, basically it points in that way.

And, you can also write it as the Pointing Vector.