In the 18th century, Benjamin Franklin discovered lightning is nature of electrical reality and the lightning rod was invented by
him in Pennsylvania in 1749.
Lightning is big electrical discharge of electricity that can reach either between the opposite charged regions within a cloud or
between the lower region of a cloud and the ground. The former event is a cloud-to-cloud discharge, while the latter, known
as cloud-to-ground lightning or simply ground strike, is much more destructive. In the case of ground strike, a downward
leader progresses from a thundercloud, it’ strong enough to hurt and kill people.
The charge distributed along the leader causes a rapid
increase in the electric field between it and the ground.
When a critical field value is reached approximately 100 m
from the earth, a ground point will launch an intercepting
upward leader. The distance at which this occurs is known
as the “Striking Distance”. Once interception occurs, the
lightning path is completed and the main discharge takes
place.
The sky is filled with electric charge. In a calm sky, the
positive (+) and negative (-) charges are evenly spaced
throughout the atmosphere. Therefore, a calm sky has a
neutral charge.
Inside a thunderstorm, the electric charge is spread out
differently. A thunderstorm is made up of ice crystals and
hailstones. The ice crystals have a positive charge, and the
hailstones have a negative charge. An updraft pushes the
ice crystals to the top of the thunderstorm cloud. At the
same time, the hailstones are pushed to the bottom of the
thunderstorm by its downdraft. These processes separate
the positive and negative charges of the cloud into two
levels: the positive charge at the top and the negative
charge at the bottom.
During a thunderstorm, the Earth’s surface has a positive
charge. Because opposites attract, the negative charge at
the bottom of the thunder cloud wants to link up with the
positive charge of the Earth’s surface.
Once the negative charge at the bottom of the cloud gets
large enough, a flow of negative charge rushes toward the
Earth. This is known as a stepped leader. The positive
charges of the Earth are attracted to this stepped leader, so
a flow of positive charge moves into the air. When the
stepped leader and the positive charge from the earth
meet, a strong electric current carries positive charge up
into the cloud. This electric current is known as the return
stroke and humans can see it as lightning.
