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• Phase velocity of an electromagnetic wave:$$v= \frac{c}{\sqrt{\varepsilon \mu}},$$ where $$c= \frac{1}{\sqrt{\varepsilon_0 \mu_0}}$$
• In a travelling electromagnetic wave:$$E\sqrt{\varepsilon \varepsilon_0} = H\sqrt{\mu \mu_0}.$$
• Space density of the energy of an electromagnetic field:$$\omega = \frac{ED}{2}+\frac{BH}{2}.$$
• Flow density of electromagnetic energy, the Poynting vector:$$S=[EH].$$
• Energy flow density of electric dipole radiation in a far field zone:$$S \backsim \frac{1}{r^2} \sin^2 \theta,.$$