A thunderstorm is one of the most impressive sights in nature with huge menacing black clouds producing hot bright flashes of lightning and booming thunder as well as torrential rain or hail. But what causes these dramatic storms and what exactly are thunder and lightning?
Clouds are formed when a mass of cold air meets a mass of warm air. 0 | F Water vapour in the warm air condenses
to form clouds. Thunder clouds are typically very tall, dark and deep. Thunder and lightning are both caused when
electrical charges build up in these clouds. 1 | However they believe that it has something to do with charged water droplets and tiny pieces of ice colliding inside the cloud. Normally a positively charged area forms in the upper region of the cloud and a negatively charged region forms in the lower region of the cloud.
These charges are incredibly large and so thunderstorms contain an enormous amount of energy. A voltage of more than 100 million volts can be generated between the cloud and the ground. 2 | Air will not normally conduct electricity
but when such huge voltages are generated, the resistance of
A Whatever you do, don’t take shelter under a tree.
B This flash of electricity is a lightning strike.
CIn fact lightning can be attracted to the same spot over and over again.
DCompare that to the voltage of the electricity supply in your home which is only about 200 volts.
E This is why lightning has its distinctive forked shape.
the air breaks down. We get a sudden spark, called an electrical discharge, which can occur inside the cloud, between the cloud and the ground, or between two
different clouds. |
3 | |
Because it is so powerful, lightning |
generates a lot of heat. A lightning strike can heat the air around it to more than 30,000 ÆC. That’s five times hotter than the surface of the sun! The heat causes the air to expand incredibly quickly and we get the loud explosive sonic boom known as thunder.
So lightning and thunder are created at more or less the same time. If you have been caught in a thunder storm, though, you will know that we normally see the lightning
first and then hear the thunder a few seconds later. 4 | The light travels so quickly that it gets to us almost instantaneously but, in air, sound takes around three seconds to travel one kilometre. This means that if we count the number of seconds between seeing the lightning and hearing the thunder and divide by three we can find out how many kilometres away the storm is from us.
It can be very dangerous to be caught outside in a thunder storm. More than 100 people are killed by lightning strikes each year in the USA alone, and many more are seriously injured. If you do find yourself in this situation the safest thing to do is to crouch down close to the ground.
5 | Lightning tends to strike at the highest point in an
area so you are much more at risk near a tree, pole, or any other tall structure. You will be safer inside a metal-bodied car, or even better inside a building. If you are inside though, it is best not to take a shower or use the phone since lightning can strike phone lines or water pipes. Whatever you do, you shouldn’t believe the saying that lightning never
strikes the same place twice. |
6 | |
Scientists observing |
thunder storms have noticed that certain tall buildings or trees can be struck a number of times, even during a single storm.
FThe warmer air is forced to rise quickly above the colder air.
GScientists don’t understand exactly how the charges are generated.
HThis is because light travels faster than sound and so the light from the lightning reaches us before the sound from the thunder.
(15 marks)
a.
Read the rubric and extract below, then listen to the dialogue and complete the notes you have made.
c.
Listen and fill in. Then, listen again and sing.