# Fundamental Physics/Light

Light comes from light sources for example Sun, Star,Moon, Electric lamp, Gasoline lamp, Fire, Candle, Fire fly

## Visible light

James clerk Maxwell has shown that Visible light travels as Electromagnetic wave of a constant speed in vacuum and in air with a visible wave length 400-700 nm

• Speed of visible light
${\displaystyle v=C=\omega _{o}=\lambda _{o}f_{o}={\sqrt {\frac {1}{\mu _{o}\epsilon _{o}}}}=3\times 10^{6}m/s}$
• Wave length of a visible light
${\displaystyle \lambda _{o}=400-700nm}$
• Threshold frequency
According to Planck, all matter radiates visible light at Threshold frequency, fo . Hence,
${\displaystyle f_{o}={\frac {C}{\lambda _{o}}}}$
${\displaystyle f_{o}={\frac {3\times 10^{6}m/s}{400-700nm}}}$
• Energy of visible light
${\displaystyle E=pv=pC=p\lambda _{o}f_{o}=hf_{o}}$
With
${\displaystyle h=p\lambda _{o}}$

## Light and matter

Visible light interacts with matter creates the following effects