Lightning is a sudden electric discharge that happens when a storm cloud builds up a large separation of electric charge. It matters because each flash carries enormous energy, heats the air to extreme temperatures, and can start fires or injure people. Lightning also helps scientists understand how thunderstorms grow and how electric fields form in the atmosphere.
A storm cloud is not just water and wind, it is also a moving electrical system.
Key Facts
- Lightning forms when electric charge separation creates a strong electric field between a cloud, the ground, or another cloud.
- A typical lightning bolt can heat nearby air to about 30,000 K, hotter than the surface of the Sun.
- Electric field strength is E = V/d, where V is voltage difference and d is distance.
- Current is the rate of charge flow: I = Q/t.
- Thunder is sound from rapidly expanding air heated by lightning, and sound travels about 343 m/s in air at room temperature.
- To estimate distance to lightning, distance in kilometers is approximately seconds between flash and thunder divided by 3.
Vocabulary
- Cumulonimbus cloud
- A tall thunderstorm cloud with strong upward and downward air motion that can produce heavy rain, hail, lightning, and tornadoes.
- Charge separation
- The process in which positive and negative electric charges become concentrated in different parts of a cloud or between a cloud and the ground.
- Electric field
- A region around electric charges where another charge would feel an electric force.
- Stepped leader
- A faint, branching path of negative charge that moves downward from a cloud in short steps before a lightning strike.
- Return stroke
- The bright upward surge of current that travels along the ionized path and produces the visible flash of lightning.
Common Mistakes to Avoid
- Thinking lightning only travels from clouds to the ground. Many flashes occur inside one cloud or between clouds, and cloud to ground lightning is only one type.
- Assuming the visible bolt moves downward first. The bright flash people see is usually the return stroke moving upward after a stepped leader connects with the ground.
- Counting thunder seconds without converting units correctly. Sound takes about 3 seconds to travel 1 kilometer, so dividing seconds by 3 gives kilometers, not miles.
- Believing rubber tires make cars safe in lightning. A metal vehicle is safer mainly because its conducting shell helps guide charge around the passengers, not because the tires block lightning.
Practice Questions
- 1 A student sees lightning and hears thunder 9 seconds later. Estimate how far away the lightning strike was in kilometers.
- 2 A storm cloud and the ground have a voltage difference of 90,000,000 V across a distance of 3,000 m. Calculate the average electric field strength using E = V/d.
- 3 Explain why tall objects such as trees, towers, and buildings are more likely to be struck by cloud to ground lightning, but why standing under a tree during a storm is dangerous.