X. Письменно ответьте на вопросы:
1. What materials are called conductors?
2. What is the advantage of copper compared with silver?
What is the most common function of wire conductors?
Why is minimum voltage drop produced in copper conductors?
What is the relation between the value of resistance and the temperature in carbon?
What materials are called insulators?
What are the most common insulators?
What are the two main functions of insulators?
ВАРИАНТ 3
I. Перепишите следующие предложения, определите в каждом из них видо- временную форму и залог глагола- сказуемого (см. Образец 1.). Переведите предложения на русский язык.
1.Faraday had many important discoveries.
2.He will have walked to school before you finish your breakfast.
3.The first permanent telephone line was built in Germany in 1877.
4.The gradual trend towards larger enterprises has not been confined to manufacturing industry.
5.The output of agricultural products is seriously affected by variations in weather conditions.
II. Перепишите следующие предложения; подчеркните в каждом из них модальный глагол или его эквиваленты. Переведите предложения на русский язык.
1.We were to inspect the new samples.
2.Maria had to make an important decision recently.
3.The driver must wear a seat belt.
4.He was allowed to borrow books from the University library.
5.We’ll be able to see each other very often.
III. Перепишите следующие предложения; подчеркните Participle I и Participle II и установите функции каждого из них, т. е. укажите, является ли оно определением, обстоятельством или частью глагола- сказуемого. Переведите предложения на русский язык.(см. образец 2.).
1.Designing new systems we can use electronic computers.
2.Having finished the experiment the engineers started a series of new tests.
3.Lake Baikal, known to be the deepest in the world, is fed by 336 rivers.
4.Farmers are cultivating wheat in this part of the country.
5.When produced at this factory the commodities have high quality and low prices.
IV. Перепишите следующие предложения и переведите их на русский язык, обращая внимание на функцию инфинитива.
1.To magnetize a body requires some energy.
2.It is important to carry out these changes as quickly as possible.
3.In order to build the power plant near Northfield (USA), three miles of tunnels were drilled.
4.This question is too complicated to be answered at once.
5.I am glad to inform you that you have been successful.
V. Перепишите следующие предложения и переведите их на русский язык, обращая внимание на герундий и его функцию.
1.A motor-starter is a device for starting motors from rest by the simple act of closing the switch.
2. I remember your having objected to this schedule.
3. Our chief is fond of travelling abroad on business.
VI. Перепишите следующие предложения и переведите их на русский язык, обращая внимание на разные значения слов to be, to have, to do.
These experiments are of great importance.
This student will have to make a report about his work.
He didn’t like their way of living.
He has already shown his office.
The contract is signed by Mr.Brown.
VII. Перепишите следующие предложения и переведите их на русский язык, обращая внимание на разные значения слов it, that, one (см. образец 3.).
1.One uses special devices to measure current, voltage, and resistance.
2.This remote control needs 4 batteries to power it.
3.The new machine works better than the old one.
4.It is well known that our Academy was founded in 1934.
VIII. Перепишите следующие предложения и переведите их на русский язык, обращая внимание на бессоюзное подчинение.
1.The report she made at the last seminar was about the life of plants.
2.At last the man we were looking for came.
3.He is the most interesting man I have ever met.
4.I’ll have translated the article you have given me by next Sunday.
IX. Переведите текст и отработайте его чтение.
Найдите в тексте:
существительные в функции определения;
инфинитив, определите его функцию;
глаголы в страдательном залоге;
прилагательные в сравнительной степени.
Transformers
A transformer is used to transfer energy. Due to the transformer electric power may be transferred at a high voltage and reduced at the point where it must be used to any value. Besides, a transformer is used to change the voltage and current value in a circuit.
A two-winding transformer consists of a closed core and two coils (windings). The primary winding is connected to the voltage source. It receives energy. The secondary winding is connected to the load resistance and supplies energy to the load.
The value of voltage across the secondary terminal depends on the number of turns in it. In case it is equal to the number of turns in the primary winding the voltage in the secondary winding is the same as in the primary.
In case the secondary has more turns than the primary the output voltage is greater than the input voltage. The voltage in the secondary is greater than me voltage in the primary by as many times as the number of turns in the secondary is greater than the number of turns in the primary. A transformer of this type increases or steps up the voltage and is called a step-up transformer. In case the secondary has fewer turns than the primary the output voltage is lower than the input. Such a transformer decreases or steps down the voltage, it is called a step-down transformer.
Compare T1 and T2 in the diagram. T1 has an iron core. For this reason it is used for low-frequency currents. T2 has an air core and is used for high frequencies.
Common troubles in transformers are an open in the winding, a short between the primary and the secondary, and a short between turns. In case a transformer has a trouble it stops operating or operates badly. A transformer with a trouble should be substituted.