Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?

The apparent delay between the sighting of lightning and the subsequent hearing of thunder arises from the significant difference in the speeds of light and sound.

1. Speed Disparity:
– Light, moving at an astonishingly high velocity of about 186,282 miles per second (299,792 kilometers per second) in a vacuum, travels at an immensely rapid pace. When lightning strikes, the emitted light swiftly reaches our eyes, virtually instantaneously, presenting itself as an immediate flash.

– Sound, in contrast, travels at a much slower pace. In the atmosphere, its speed is approximately 1,125 feet per second (343 meters per second) at room temperature. This speed varies slightly based on factors like temperature and humidity.

2. Spatial and Temporal Gap:
– When lightning occurs, it generates an intense burst of light. Because light travels so swiftly, the illumination reaches our eyes almost instantly, causing us to perceive the lightning immediately.

– Thunder, however, originates from the rapid expansion and contraction of air around the lightning bolt due to the immense heat. As sound moves comparatively slower, it takes time to propagate through the air to reach our ears.

– Estimating the time lapse between observing the lightning and hearing the thunder, factoring in the speed of sound, allows for an approximate calculation of the lightning’s distance. Each five-second interval between lightning and thunder corresponds to roughly one mile of distance.

Consequently, the delay experienced between witnessing the lightning and hearing the thunder is a consequence of the substantial difference in the speeds of light and sound. The lightning’s luminance reaches us almost instantly, while the sound, moving more gradually, creates the delay in perceiving the thunder.