|Why does lightning occur? Why does lightning have
branches? Does lightning only form in storms? Does
every strike of lightning hit the ground?
These are some interesting questions that you have
asked. I'll try to answer all four of them for you
and hopefully they'll give you some more insight
First, lighting occurs due
to an accumulation of charge, electrons if you
like, in the air. As a storm grows, electrical
charges build up in the clouds. At the same time,
oppositely charged particles are growing in number
on the earth's surface. As you know opposite
charges attract and due to the large number of
charges this attraction grows quickly. At some
point the attraction becomes large enough to
overcome air's resistance to electrical flow, in
this case the flow of charges between the ground
and the clouds. These particles move toward each
other at incredible speeds and when they meet they
complete an electrical circuit. Charge from the
ground then surges upward at nearly one-third the
speed of light and we see a bright flash of
Now to answer your final
question, the lightning starts at the ground and
moves upward, it is just moving too fast to be
able to tell this.
If you have a stream of
weakly charged particles moving through the air,
sometimes the particles will split from each other
trying to find the path of least resistance
through the air. When this happens, branches will
form and this is what people call branch or forked
Now does lightning only occur in
storms, I am not sure. I would think that
lightning could occur any time there was enough
charge built up in the clouds. However, I would
guess that only during storms would this occur.
Lightning is, simply put, a giant spark of
electricity. As you probably know, even matter
that is not electrically charged is made up of
components which are both positively and
negatively charged. For some reason I don't
understand (and, I am told, is not well
understood) these charges will separate in a storm
cloud -- resulting in different regions of the
cloud having different electrical charges.
Usually what happens is that electrons (which
have negative charge) build up on the bottom
surface while protons (having positive charge) are
at the top.
The negative charges on the bottom
of the cloud can pull on the positive charges in
the ground and repel the negative ones. The result
is that the ground surface becomes positively
charged also. As the charges build up more and
more, the situation eventually becomes very
unfavorable and one of two things can happen.
Either the electrons in the cloud will suddenly
jump toward the protons at the top of the cloud
(known as "sheet lightning") or the electrons will
find their way to the ground. The electrons
flowing to the ground are so energetic that they
excite the air which causes it to glow. That is
what you see as lightning. Apparently, the air can
get as hot as 55000 degrees Fahrenheit!
not every strike of lightning hits the ground.
Often there are lightning strikes between clouds
or between one part of a cloud to another.
Sometimes lightning can start from the ground --
these strikes appear to have the branches pointing
upward instead of downward. I believe they are
very rare and usually occur from tall
By the way, there is more to
lightning than just lightning. In 1990, it was
discovered that during lightning strikes, large
red flashes (called "red sprites") can be seen
from above the thunder cloud. And in 1995, tall
cones of blue light were discovered (called "blue
jets") above thunderclouds also. As far as I know,
nobody understands what these are or how exactly
they relate to lightning. Lightning is on the
forefront of scientific knowledge!
Lightnings, are caused by an electric discharge
between the clouds and the earth (in most cases) .
Electric charges accumulate in the clouds
through the friction of water molecules which are
present in great numbers in the clouds. This
reservoir of electric charges has to eventually
empty itself somewhere. It will do so by
establishing an electric discharge through the
atmosphere and towards the earth and this is the
path followed by the lightning you see.
electric potential (energy associated with all the
electric charges) of the cloud is larger than that
of the earth and therefore charges will flow from
the high potential reservoir (the cloud ) to the
earth (at lower potential. Much like water will
fall from a high water lake to a lower basin by
forming a cascade or a river.This electric
discharge path ionizes the molecules (molecules
which have lost of number of electrons) in the
atmosphere between the clouds and the earth
surface. When a molecule in the air is ionized it
will glow and this is why you see light associated
with the lightning.
Have you also noticed that
sometimes when you are in an airplane and fly over
a thunderstorm that there are also lightnings that
do not go towards the earth but instead go
Have you also noticed that there
are lightning in the sky during summer nights even
though there is no thunderstorm??.
lightnings also do not go towards the earth but
propagate between clouds. Try to guess why and
give an explanation. .
Please check out the web page on lightning that
two of my students in Physics 2 last spring
It is very informative and has beautiful
pictures! I think you will find it interesting and
you will have your questions answered.
quite good. I think all these questions will be
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