Question

The unit of poynting vector is:
A) ${Watt}$
B) ${Joule}$
C) ${{Watt} \over {{m^2}}}$
D) ${{Joule} \over {{m^2}}}$

Answer 1

A poynting vector gives the measure of the energy transfer of flux per unit area per unit time. The time gets multiplied with energy to give power. So eventually the formula for poynting vectors becomes power per unit area. The unit of power is watt and area is ${{m^2}}$.

Complete step by step answer:
The unit of poynting vector is ${{Watt} \over {{m^2}}}$.
A poynting vector is defined as the directional energy flux of an electromagnetic field. Energy flux is the energy transferred per unit area per unit time. Flux of an electromagnetic field is defined as the total number of field lines passing through a closed surface. Its unit is $weber$.

An electromagnetic wave is the combination of magnetic and electric waves. For example light etc. For any electromagnetic wave flux is a major property for it. It gives the density of the wave. More the denser the flux more it will have strength. It also depends on the source from where the electromagnetic wave is generating. Each source has different intensity.

Note: Usually one gets confused with the definition and unit. The unit should consist of joules in it. But the unit of poynting vectors is ${{Watt} \over {{m^2}}}$. This is because it is actually energy per unit area per unit time. So the unit becomes power per unit area.