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WHO DISCOVERED ELECTRICITY?
The story of the discovery of electricity is connected with the name of Thales, the Greek philosopher. The story goes that one day Thales rubbed a piece of amber against his sleeve and found to his great surprise that it attracted small bits of dried leaves. After further experimenting he concluded that this attractive force was a property that amber alone possessed.He called this characteristic "electricity" because the Greek word for amber was electron.
Thales' great discovery remained a curiosity for more than twothousand years. Then many other substances were found to have this curious property of electricity too. Naturally the peopleof the past had no idea of what electricity was. They thought of it as "rays" or "stream" that passed from the rubbed material. There were scientists who thought electricity to be a sort of "fluid" that flowed through wires as water flows through pipes. Later many of them found out that electricity was made of tiny particles of some kind. In this way they tried to separate electricity into individual particles. There were some attempts to weigh a single particle of electricity and calculate its electric charge. This was one of the most delicate weighing jobs ever done by a man, for a single electric particle weighs only about half a millionth of a millionth of a millionth of a millionth of a millionth of a pound. To make up a pound, it would take more of those particles than there are drops of water in the Atlantic Ocean. Now we know these electric particles to be electrons.
When a large number of electrons break away from their atoms and move through the wire, we describe this action by saying that electricity is flowing through the wire and the electrical "fluid" that scientists of the past talked about is nothing else than electrons flowing along a wire. A lot of scientists worked in the field of electricity doing their best to make the life of people good and happy.
ELECTRIC SHOCK SAFETY ELECTRIC SYSTEM.
The strength of current depends on both the voltage and on the resistance in a circuit. A current of 50ma is dangerous for a man, it may result in an electric shock. One gets an electric shock in case one touches live conductors when the power is on. And a current of l00ma and higher is lethal. Thus, before working on a circuit, deenergize it and work on it with the power off.
Earthing system serves to protect attending personnel from electric shocks when voltage appears on parts that are normally dead. The risk of an electric shock decreases with decreasing voltage. In wet and hot atmosphere the risk of electric shock increases. Safe voltage for circuits used in dry atmosphere is under 36V. When the power is on contacts with live conductors are dangerous for life. When a live conductor is touched with both hands the resistance of the conductor is from 10,000 to 50,000 ohms. When a live conductor is touched with one hand the resistance is much higher. The higher is the body resistance, the smaller is the current that flows through the body. Take it into consideration and work with one hand if the power is on! Or work on the circuit with the power off!
Thus measures are taken to protect attending personnel from contacts with live parts of installations under voltage.
The danger of electric shock disappears provided the metal parts of installations under voltage are connected with ground by means of safety earthing. Connecting to ground is made by means of measuring devices. The faulty parts should be detected, eliminated, and replaced by new ones.
ВАРИАНТ № 1
I. Выберите правильный ответ, обращая внимание на особенности модальных глаголов и их эквивалентов. Переведите предложения на русский язык:
1.1. Before beginning an experiment one … carefully read all the instructions.
a) are able to
b) were allowed to
c) should
1.2. You … check a fuel level in the car tomorrow.
a) are able to
b) will have to
c) were to
1.3. The scientist … analyze the results of the test.
a) have to
b) might
c) should
1.4. We … say that the discovery of atomic energy is as important as the discovery of fire.
a) is to
b) will be able to
c) can
1.5. The machine tool which … perform turning is called the lathe.
a) is to
b) could
c) are able to
II. Выберите правильный ответ, обращая внимание на видовременную форму и залог сказуемого, и переведите предложения на русский язык:
2.1. Soon the operation of the conveyor … by outer factors.
a) are not influenced
b) were not influenced
c) will not be influenced
2.2. The engineers at our plant … into operation this automatic assemble line by the beginning of the new year.
a) will put
b) have put
c) will have put
2.3. An interesting phenomenon in the field of aerodynamic effects … by Russian scientists last year.
a) are discovered
b) will be discovered
c) was discovered
2.4. The great Russian scientist Alexander Lodygin … the first incandescent lamp in 1873.
a) had produced
b) was produced
c) produced
2.5. At 8 o’clock tomorrow they … for a very important experiment.
a) will be prepared
b) will be preparing
c) will prepare
III. Выпишите предложения, содержащие причастия I и II, подчеркните причастия. Переведите предложения на русский язык.
3.1. Going into chemical combinations elements entirely change their properties.
3.2. The machine parts lie on a moving platform.
3.3. Unless tested the machine must not be put into operation.
3.4. When heated the polymer changed its properties completely.
IV. Прочитайте и УСТНО переведите текст, затем выполните тест по тексту:
The Microwave Oven
The first microwave oven was very big and heavy. At first, it was used exclusively in restaurants, railroad cars and ocean liners — places where large quantities of food had to be cooked quickly. In fact, it took decades after the invention of the microwave oven for it to be refined to a point where it would be useful to the average consumer.
A large increase in the use of microwave ovens has created a greater need for effective product design for microwave heating which ensures microbiological safety while maintaining product quality.
During conventional heating methods, the primary mechanism of heat transfer is either conduction or convection, depending of the nature of the food. In the microwave foods heat from the generation of heat within the food itself, not from the conduction of heat energy from hot air to the outer layer of the cooler product.
Microwaves penetrate the food and transfer their energy to dipolar or ionic molecules, which are present in all foods. The greater the concentration of dipolar molecules within particular areas in a food product, the faster that area of the product will heat. Some of this heat energy is transferred to cooler areas by conduction or convention, so helping the heating of other cooler areas, i.e. those areas which are less receptive to microwave heating.
The penetration depth of microwave energy depends on how rapidly the microwave energy is absorbed by the food product. If most of the energy is transferred to molecules at the surface of the product, the penetration will be shallow, with the bulk of the food heating mainly by convection or conduction.
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