Контрольная работа для студентов 4 курса технических специальностей.
Electricity.An electric current is flow of electricity. There are two kinds of electricity: positive and negative. Glass rubbed with is positively charged, ebonite rubbed with fur is negatively charged. Like charge repel, unlike charges attract. The leaf electroscope is used to detect, distinguish and measure charges. The ultimate particle of negative electricity is called the electron; that of positive electricity is called the proton. It has been known for centuries that certain black, heavy stones have the property of attracting iron, this property being called magnetism. A body that exhibits magnetism is called a magnet. The two types of a magnet that show the strongest magnetism are called the North Pole and the South Pole. Magnets not only affect ordinary iron, but they affect one another. When a pole of one magnet is brought toward a pole of the second magnet, they will repel if both are north poles or both are south poles, they will attract if one is a north pole and the other a south pole.
The region in which magnetic forces act is called a magnetic field. When placed in a strong magnetic field, iron becomes magnetized. Electricity and magnetism are closely connected. Almost all metals are good conductors of electricity, with copper being one of the best conductors of all. Glass, paper, rubber are the most common non-conductors or insulators.
According to their conductivity all materials are divided into conductors, insulators and semiconductors. A conductor owes its conducting powers to the presence of free electrons which have broken away from their atoms. The most common of them are metals, carbon electrolytes. According to their resistivity, conductors are divided into two groups: the first includes materials with low resistivity; copper, aluminum and others. These metals are used to produce wire conductors due to their high mechanical strength. The second group includes materials with high resistivity: one of these is nichrome. Due to its good heat resistance, nichrome is used to produce heaters. Insulating materials have a very low conductivity. They offer extremely high resistance to the flow of current. Insulators are divided into gaseous, liquid, and solid. They are also divided into groups according to their heat resistance. The semi- conductor is a material whose conductivity ranges between that of conductors and non-conductors of insulators. While the conductivity of metals is very little influenced by temperature, the conductivity of semi-conductors increases sharply with heating and falls with cooling. This dependence has opened great prospects for employing semi-conductors in measuring techniques.
There are several factors that determine the electrical resistance of any wire:
-the material which it is composed of;
-the size of the wire;
-its temperature. In more general terms, the resistance of a wire is proportional to its length and inversely proportional to its cross-sectional area. This is Ohm1s law.
1.Замените русские слова в скобках на английские:
Magnetism is the (свойство) of attracting iron.
Every magnet has two (полюса): the (северный) pole and the (южный) pole.
Magnet (влияют) one another.The North Pole of one magnet (отталкивает) the North Pole of another magnet. It is the same with the South Pole.
The North Pole of one magnet (притягивает) the South Pole of another magnet.Almost all metals are good (проводники) of electricity.
2.Переведите и задайте вопросы к следующим предложениям:
Semi-conductors find wide application in designing electronic counters, because they react to all kinds of radiations. (Where?).One of the main engineering problems which could be solved by using semi-conductor was converting heat into electricity without using boilers or other machines. (What?).
3.Перестройте следующие предложения, употребив Passive. Переведите:
Our explorers discover rich coal deposits in Yakutia.
They find many valuable minerals there.
My sister sent the letter yesterday.
We will meet the delegation tomorrow.