The frequency of the power wave associated with an electromagnetic wave having an E field as \(E = {e^{ - z/\delta }}\cos \left( {\omega t - \frac{z}{\delta }} \right)\), is given by

• A. \(\frac{\omega }{{8\pi }}\)
• B. \(\frac{\pi }{{4\pi }}\)
• C. \(\frac{\omega }{{2\pi }}\)
• D. \(\frac{\omega }{\pi }\)