Why are lightning bolts jagged instead of straight?
William C. Valine, an atmospheric scientist at the University of Arizona, explains. Ever since Benjamin Franklin’s time lightning has been understood to be a large electrical discharge similar to that seen when a conductive object (like a metal doorknob) is touched after a static electric charge is picked up (by feet scuffing across carpet, for example). But whereas the spark from static electricity measures a centimeter or less in length, a lightning channel can span five kilometers or more. (Also, cloud-to-ground lightning involves electrical currents on the order of tens of thousands of amps. In contrast, a circuit breaker for a common household circuit is usually rated at 20 amps.) Because of its extreme scale, lightning is a complex physical phenomenon. During a thunderstorm the lower portion of a cloud contains a region that accumulates a large negative charge and the upper portion becomes positively charged. Also, a positive charge is induced on the surface of the earth, because
