Comprehension check
Date: 2015-10-07; view: 597.
Translate the sentences.
Catching a Plane
Open the brackets. Put the verbs in Present Simple Active or Present Simple Passive.
When you (to arrive) at an airport, you should go straight to the check-in desk where your ticket and luggage (to check). You (to keep) your hand luggage with you but your suitcases (to take) to the plane on a conveyor belt. If you are at international flight, your passport (to check), and then you and your bags (to x-ray) by security cameras. Sometimes you (to give) a body search and your luggage (to search) by a security officer. You (to wait) in the departure lounge until your flight (to call) and you (to tell) which number gate to go. Finally you (to board) your plane and you (to show) your seat by a flight attendant.
1. На английском языке говорят по всему миру. 2. Эти часы производят в Швейцарии. 3.Меня никогда не приглашают на вечеринки. 4. Моему брату всегда дарят много подарков. 5. Вам часто задают этот вопрос? 6. Яблоки собирают осенью? 7. На скольких языках говорят в Индии? 8. В Россию импортируется много фруктов. 9. В Китае едят много риса. 10. Эти автомобили не производятся в Германии.
10. Correct the sentences if it is necessary.
1. Each electric particle projects into space a field of electric force, and as the particles move along a wire, the lines of force move with them.
2. A variable electric field is never accompanied by a magnetic field; and conversely, a variable magnetic field is always accompanied by an electric field.
3. The joint interplay of electric and magnetic forces is what is called an electromagnetic field: it is not distributed continuously in space; in a vacuum it propagates at the speed of light (300 km/sec); it interacts with charges and currents to convert itself into other forms of energy (chemical, mechanical, etc.).
4. The theory of the electromagnetic field was stated by the Scotch physicist James Clerk Maxwell in his "Electricity and Magnetism" published in 1873.
5. In the case of a stationary charged body the magnetic fields, built up by the elementary charges constantly moving inside it cancel each other, and there is magnetic field.
6. A measure of the strength of an electric field is given by the mechanical force per unit charge experienced by a very small body placed in this field and is denoted by the letter F.
7. If the strength of an electric field is the same both in magnitude and direction at any point in space, the field is called nonuniform.
8. It is relevant to note that quantities which have both magnitude and direction are called scalars, as distinct from quantities which have only magnitude and are called vectors.
9. The total number of lines of electric force through a surface placed in an electric field is called the surface charge density and is denoted by the letter N.
10. Placing a negative charge at definite point in the field set up by a positively charged spherical body, it is possible to obtaina set of such paths, or lines of electric force.
11. Like charges are known to attract one another.
12. The surface charge density depends on the quantity of electric charge on a given body and on the shape of the letter.
11. Use the text to answer the following questions:
1.What is an electromagnetic field?
2.What properties has the electromagnetic field?
3.What condition enables us to investigate electric and magnetic fields separately?
4.What quantities are called vectors (scalars)?
5.What is an electric flux?
6.In what way can we determine the electric flux of a uniform field?
7.What is the strength of an electric field?
8.What is the surface charge density?
9.On what does the surface charge density depend?
10.How is the strength of a magnetic field measured?
12. Put the jumbled sentences in the logical order to sum up the contents of the text.
1. Modern physics defines the electromagnetic field as a distinct form of matter possessing definite properties.
2. The theory of the electromagnetic field was stated by the Scotch physicist James Clerk Maxwell in 1873.
3. If the strength of an electric field is the same both in magnitude and direction at any point in space, the field is called uniform.
4. An inertialess charge placed in an electric field would follow a path called a line of force.
5. It is the motion of these lines of electric force that sets up a magnetic field transverse to them.
6. Typical vectors are force, velocity, acceleration, while typical scalars are temperature, quantity of matter, energy, power.
7. The density of lines of force will give a graphic idea of the field strength.
8. The particles move along a wire, the lines of force move with them.
9. In the case of a stationary charged body the magnetic fields, built up by the elementary charges constantly moving inside it cancel each other, and there is practically no magnetic field.
10 The joint interplay of electric and magnetic forces is what is called an electromagnetic field and is considered to have its own objective existence apart from any electric charges or magnets with which it may be associated.
11. The joint interplay of electric and magnetic forces is what is called an electromagnetic field: it is distributed continuously in space; in a vacuum it propagates at the speed of light (300,000 km/sec); it interacts with charges and currents to convert itself into other forms of energy (chemical, mechanical, etc.).
12. Quantities which have both magnitude and direction are called vectors, as distinct from quantities which have only magnitude and are called scalars.
13. The quantity of electricity per unit area is called the surface charge density.
14. Each electric particle projects into space a field of electric force.
15. A measure of the strength of an electric field is given by the mechanical force per unit charge experienced by a very small body placed in this field and is denoted by the letter E.
16. For a nonuniform field the flux is determined in a different way.
17. The total number of lines of electric force through a surface placed in an electric field is called the electric flux and is denoted by the letter N.
18. It depends on the quantity of electric charge on a given body and on the shape of the latter.
13. Read the text and translate it into Russian, fulfill the tasks given in Comprehension check.
If two metal spheres on insulating supports are charged with unlike electricity (say, sphere A positively and sphere B negatively) and connected by a metal conductor, electrons will flow from B, where they are in excess, to A where they are lacking. The flow of electrons in a conductor is called an electric current.
If sphere A is continuously charged with positive electricity and sphere B with negative electricity, there will be a continuous flow of electric current in the conductor. While in motion along a conductor, electrons collide with other electrons, atoms or molecules. As a result of these impacts, energy is released in the form of heat, and the motion of electrons along the conductor is impeded. This opposition to the motion of electrons along the conductor is known as the electrical resistance of the conductor.
There are several factors that affectresistance.
Resistance varies with the atomic structure or nature of the conducting material. Good conducting materials such as silver, copper, and aluminium have low resistance. Cast iron and nichrome (an alloy of iron, nickel, and copper) are considered to be the examples of poorer conducting materials.
The resistance of most metals varies directly with temperature. The resistance of metals increases with increasing temperature, while that of liquids and carbon decreases. There are several metals, however, such as manganin, constantan, nickeline, etc., whose resistance remains practically unaffected by temperature rise.
The resistance of a conductor increases in direct proportion with its length. That is, temperature being constant, the resistance will be doubled if the length of the conductor is doubled.
The resistance of the conductor varies inversely with its cross-section area.
The unit of electrical resistance is the ohm. The resistance in ohms of a conductor 1 metre long and 1 mm2 in cross-section is called resistivity and is designated by the Greek letter 
(rho).
The resistance of a conductor can be found from the equation R= 
where
R— resistance of the conductor in ohms;
— resistivity of the conductor, ohm-mm2-m;
I— length of the conductor in metres;
S— cross-section area of the conductor in mm2.
The change in the resistance of a conductor per ohm of the initial resistance and per degree change of temperature is termed the temperature coefficient of resistance and is designated by the letter α:
α = 
where
R0— initial resistance of the conductor;
Rt— final resistance of the conductor;
tQ— initial temperature of the conductor;
t — final temperature of the conductor.
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