Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?
The speed of light in air is 3 x 10 8 m/s.
The speed of sound in air is 340 m/s.
Since the speed of light is much more as compared to the speed of sound in air, lightning travels faster than the thunder.
Hence, even though they occur at the same time, lightning is seen earlier than thunder can be heard.