Where Does the Thunder Come From?

Where does the thunder (and lightning) come from? The basic idea is that thunder clouds can become giant Van de Graaff generators and create huge charge separations within the cloud. Let's look at how it works.

Clouds contain millions and millions of water droplets and ice particlesthat are suspended in the air. As the process of evaporation and condensation occurs, these droplets collide with other moisture that is condensing as it rises. The importance of these collisions is that electrons are knocked off of the rising moisture, creating a charge separation. The newly knocked-off electrons gather at the lower portion of the cloud, giving it a negative charge. The rising moisture that has lost an electron carries a positive charge to the top of the cloud.

As the rising moisture encounters colder temperatures in the upper cloud regions and begins to freeze, the frozen portion becomes negatively charged and the unfrozen droplets become positively charged. At this point, rising air currents have the ability to remove the positively charged droplets from the ice and carry them to the top of the cloud. The remaining frozen portion either falls to the lower portion of the cloud or continues on to the ground.

The charge separation has an electric field associated with it. Like the cloud, this field is negative in the lower region and positive in the upper region. The strength or intensity of the electric field is directly related to the amount of charge build-up in the cloud. As the collisions and freezing continue to occur, and the charges at the top and bottom of the cloud increase, the electric field becomes more and more intense – so intense, in fact, that the electrons at the Earth's surface are repelled deeper into the Earth by the negative charge at the lower portion of the cloud. This repulsion of electrons causes the Earth's surface to acquire a strong positive charge.

All that is needed now is a conductive path so the negative cloud bottom can conduct its electricity to the positive Earth surface. The strong electric field creates this path through the air, resulting in lightning. The lightning is a high-voltage, high-current surge of electrons, and the temperature at the core of a lightning bolt is incredibly hot. For example, when lightning strikes a sand dune, it can instantly melt the sand into glass. The combination of the rapid heating of the air by the lightning and the subsequent rapid cooling creates sound waves. These sound waves are what we call thunder. There can never be thunder without lightning.

 

Exercise 12. Divide into small groups. Make and write down on a separate sheet of paper 10 True / False sentences on the text. Exchange it with the other group. Prove your point of view.

 

Exercise 13. Make up 10 questions on the text and answer your partner’s questions.

 

Exercise 14. From physical point of view give some information about

· rainbow;

· tides;

· hurricanes;

· rains;

· greenhouse effect.

 

Unit 2

 

GRAMMAR: Modals

TEXTS: “Physics Lab Safety Rules”; “Our Place in the Universe”

MODAL VERBS

Present	Past	Future
can (фізична можливість, можливість, дозвіл, вирогідність) I can translate this text easily. Can you pass the salt, please? to be able to (здатний) He is a great sportsman, he is able to swim over the English Channel.	could (можливість дії, менша вірогідність у порівнянні із can) They could miss the train but fortunately they were on time at the station.   was / were able to (можливість, здатність) The child was not able to read the book, he was too small.	‑   will be able to (можливість, здатність) As soon as you finish the work, you will be able to go out.
must (повинен, моральне зобов’язання) People must take care about their old parents. to have to (вимушений, повинен за обставинами) We have to work under awful conditions. to be to (повинен згідно з попереднім планом, домовленості) Students are to take exams at the end of the term. What am I to do?	‑   had to He had to carry out experiments without anyone’s assistance.   was / were to My neighbour was away and I was to feed his cat and water the flowers.	‑   will have to We will have to translate the article. Nobody will do it for us.   ‑
may (дозвіл, вірогідність) The work has been done. You may be free.     to be allowed to (дозвіл) You are not allowed to leave your place without permission.	might (вірогідність менша у порівнянні із may) They might be there but I’m not sure. was / were allowed to (дозвіл) There were not allowed to go to the party.	‑     will be allowed to (дозвіл) You will be allowed to go out if you tidy up everywhere.
should (слід, порада, рекомендація) You should wear safety glasses in the laboratory.
ought to (слід, використовується як синонім should) You ought to revise for your test.
need (використовується у заперечній формі із значенням відсутність необхідності) He didn’t need to take a taxi as I gave him a lift.
Would (1) звичайна дія у минулому, що повторювалася, синонімічно до used to; 2) сильне небажання виконувати якусь дію; 3. властива дія (у технічних текстах) He would go to the country every summer in his childhood. I asked him to do it but he wouldn’t. Paper would burn well.

 

Exercise 1. Fill in the blanks with "to have to", "to be to", "must" according to the meaning.

1. The experiment... take place on Monday, I think everything is ready.
2. They... examine this sample under a very powerful microscope as it is very small: 3. I am very tired, I... have a rest. 4. Our meeting... take place after our last lecture. 5. You... work hard if you want to finish this work. 6. I.... go to the reading-room as I have no books at home. 7. He... wait for two hours as his train has just left. 8. All the students of our Institute... carry out a number of experiments in the laboratory.