This is because velocity of sound in air is only 332 m/s, whereas velocity of light is 3 x ${{10}^{8}}$ m/s. Hence the flash is seen much before the thunder of lightening is heard.
This is because velocity of sound in air is only 332 m/s, whereas velocity of light is 3 x ${{10}^{8}}$ m/s. Hence the flash is seen much before the thunder of lightening is heard.