The Poynting vector of plane EM wave traveling in a medium represents Select one:a. Powerb. Power Densityc. Energyd. Energy Density

Break Down the Problem

1. Identify what the Poynting vector represents in the context of electromagnetic (EM) waves.
2. Consider the definitions of the terms given in the options: Power, Power Density, Energy, and Energy Density.

Relevant Concepts

• The Poynting vector $\mathbf{S}$ is defined as: $\mathbf{S} = \frac{1}{\mu_0} \mathbf{E} \times \mathbf{H}$ where $\mathbf{E}$ is the electric field vector, $\mathbf{H}$ is the magnetic field vector, and $\mu_0$ is the permeability of free space.
• The Poynting vector indicates the direction and magnitude of energy flow per unit area.

Analysis and Detail

1. Power refers to the total energy used or transferred per unit time, but it does not specify how that energy is distributed over an area.
2. Power Density refers to the power per unit area, which aligns closely with the definition of the Poynting vector as it describes how power is distributed.
3. Energy is a broader concept and does not precisely capture the conveyance of energy in wave terms.
4. Energy Density refers to the amount of energy stored in a given system or region of space per unit volume, which differs from the flow of that energy.

Verify and Summarize

The definition of the Poynting vector and its relationship with electrical and magnetic fields leads to the conclusion that it represents the flow of energy per unit area (power density), not just power or energy.

Final Answer

The correct answer is b. Power Density.