Question

Why thunder is heard a few seconds after the flash is seen?

Answer 1

1. The speed of light $(3\times {10}^{8}m/s)$ is very high compared to the speed of sound $(345m/s)$. The light takes very less time to reach the earth's surface as compared to sound. That is why a flash of thunder is seen prior to the sound of thunder.
2. At the time of Lightning, flash, and thunder are emitted at the same time. As the light travels faster than the sound, the flash can be seen almost at the time of lightning. But the sound of thunder is heard after a few seconds of lightning.