Electromagnetic Waves formulas

Formulas

Displacement current

$\displaystyle i_d = \varepsilon_0\frac{d\Phi_E}{dt}$

Speed in vacuum

$\displaystyle c = \frac{1}{\sqrt{\mu_0\varepsilon_0}} = 3\times10^8\ \text{m/s}$

Speed in a medium

$\displaystyle v = \frac{1}{\sqrt{\mu\varepsilon}}$

Ratio of the fields

$\displaystyle \frac{E_0}{B_0} = c$

Wave relation

$\displaystyle c = \nu\lambda$

Energy density

$\displaystyle u_{\text{av}} = \tfrac12\varepsilon_0E_0^2$

Spectrum, longest to shortest wavelength

• Radio, microwaves, infrared, visible, ultraviolet, X-rays, gamma rays.
• Frequency and photon energy increase in the same order.
• Visible light runs from about 400 nm (violet) to 700 nm (red).
• E, B and the direction of travel are all perpendicular to each other.