Light travels at a constant speed of 3.00 x 10 to the 8th power m/s, whereas sound travels through the air at a constant speed of 340 m/s.
a) How long does it take for light to travel from a lightning strike to an observer 1.00 km away?
b) How long after the flash is seen is the thunder produced by the lightning heard?

Time for light to travel 1 km = 1000/3 x 10(8th) = 3.33 x 10(-6th) = 0.0000033 secs
Time for thunder to travel 1km = 1000/340 = 2.94 sec