Formula Phase Velocity of a Wave Wavelength Period
$$\class{blue}{ v_{\text p} } ~=~ \frac{ \class{red}{ \lambda } }{ T }$$ $$\class{blue}{ v_{\text p} } ~=~ \frac{ \class{red}{ \lambda } }{ T }$$ $$\class{red}{ \lambda } ~=~ \class{blue}{ v_{\text p} } \, T$$ $$T ~=~ \frac{ \class{red}{ \lambda } }{ \class{blue}{ v_{\text p} } }$$
Phase velocity
$$ \class{blue}{ v_{\text p} } $$ Unit $$ \frac{\mathrm m}{\mathrm s} $$ Phase velocity indicates the velocity of points of the same phase. For example, if you focus on a wave crest, then the phase velocity is the velocity of that wave crest.
The phase velocity of electromagnetic waves is the speed of light \(c\).
Wavelength
$$ \lambda $$ Unit $$ \mathrm{m} $$ For example, wavelength is the distance between two wave crests.
Period
$$ T $$ Unit $$ \mathrm{s} $$ Period is the time a wave crest takes to travel the distance \(2\pi\).