If the thunder is heard 20 seconds after a lightning flash, how far away is the storm in miles?

• A. 2 miles
• B. 4 miles
• C. 6 miles
• D. 8 miles

Answer: (B)

Thunder distance is estimated from the time delay between the lightning flash and the accompanying thunder, because sound travels at a finite speed. A handy rule is that sound moves about 1 mile in roughly 5 seconds, so every 5-second interval equals about 1 mile of distance. If the thunder arrives 20 seconds after the flash, the storm is about 4 miles away. This is a practical estimate; actual distance can vary slightly with temperature because the speed of sound changes, but 4 miles is the standard takeaway here.