Page 3 - Reading Success B8

From early on, man has wondered about the great power and destructive capacity of
lightning. It is one of nature’s most stunning spectacles, dramatically lighting the dark sky
during a thunderstorm. Scientists estimate that in one year there are approximately 16

million thunderstorms across the world. As many as 1,800, can take place at any given
moment. Scientifically lightning is a visible discharge of atmospheric electricity. If a giant
spark leaps from one part of a thundercloud to another, it appears as sheet lightning.
However, if a spark travels from a cloud to the ground it appears as forked lightning.

It is unknown how electricity is formed within a thundercloud. Scientists believe it is
caused by the collisions of the many water droplets found inside a thundercloud. In theory,
descending water drops hit smaller water drops, causing some of the energy in the small
drops to transform into a charge of positive electricity in the larger drop. This positive charge

causes the surrounding air to gain an opposing, negative charge. As the drop falls it is
condensed by the moisture in the air causing it to grow bigger. When the drop grows to a
size of about a fifth of an inch across, it splits in two, each half still carrying its positive

charge.

If these drops simply fell straight to the earth, the charge would have no effect. However,
inside a thundercloud are powerful drafts of air which carry the drops up, causing the entire

process to be repeated many times. As the charges on these drops increase, the
thundercloud collects and stores electricity. After about 15 minutes the charge stored in the
cloud is large enough to break down the covering of air around it. This causes a lightning
flash to occur.

Thunder is caused when lightning heats the air around it to temperatures up to 300,000
degrees Fahrenheit - three times the temperature of the sun’s surface. This makes the air
expand and then explode. The flash of light caused by the lightning travels faster than
the sound of the explosion ; so by counting the gap between seeing the lightning flash and

hearing the thunder one can estimate the distance of the lightning. A five second delay
roughly equals a distance of one mile.

Main Idea

What is the main idea of this story?

a. the cause of thunder

b. the different types of lightning
c. how lightning is possibly formed
d. the causes of thunderstorms

6_Reading Success B 8