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ПРАКТИЧЕСКОЕ ЗАНЯТИЕ 13




Электромагнетизм

Electromagnetism

Теоретическая часть

Данный лексический материал предназначен для того, чтобы студенты могли свободно ориентироваться в научном тексте и активно использовать предлагаемые слова и словосочетания.

Задание 1. Выучите следующие слова и словосочетания:

relationship отношение

to stumble upon натолкнуться

wire проволока

to suspend подвешивать

compass needle стрелка компаса

to confirm подтверждать

serendipitous неожиданный

direction направление

magnetic flux line линия магнитной индукции

to surround окружать

current ток

to deflect отклонять

coil катушка

force сила

to multiply умножать

conductor проводник

obvious очевидный

switch выключатель

to actuate приводить в действие

Задание 2. Прочитайте и переведите текст:

Electromagnetism

The discovery of the relationship between magnetism and electricity was, like so many other scientific discoveries, stumbled upon almost by accident. The Danish physicist Hans Christian Oersted was lecturing one day in 1820 on the possibility of electricity and magnetism being related to one another, and in the process demonstrated it conclusively by experiment in front of his whole class! By passing an electric current through a metal wire suspended above a magnetic compass, Oersted was able to produce a definite motion of the compass needle in response to the current. What began as conjecture at the start of the class session was confirmed as fact at the end. Needless to say, Oersted had to revise his lecture notes for future classes! His serendipitous discovery paved the way for a whole new branch of science: electromagnetics.

Detailed experiments showed that the magnetic field produced by an electric current is always oriented perpendicular to the direction of Sow. A simple method of showing this relationship is called the left-hand rule. Simply stated, the left-hand rule says that the magnetic flux lines produced by a current-carrying wire will be oriented the same direction as the curled fingers of a person’s left hand (in the “hitchhiking” position), with the thumb pointing in the direction of electron flow. The magnetic field encircles this straight piece of current-carrying wire, the magnetic flux lines having no definite “north” or “south” poles.

While the magnetic field surrounding a current-carrying wire is indeed interesting, it is quite weak for common amounts of current, able to deflect a compass needle and not much more. To create a stronger magnetic field force (and consequently, more field flux) with the same amount of electric current, we can wrap the wire into a coil shape, where the circling magnetic fields around the wire will join to create a larger field with a definite magnetic (north and south) polarity.

The amount of magnetic field force generated by a coiled wire is proportional to the current through the wire multiplied by the number of “turns” or “wraps” of wire; in the coil. This field force is called magnetomotive force (mmf), and is very much analogous to electromotive force (E) in an electric circuit.

An electromagnet is a piece of wire intended to generate a magnetic field with the passage of electric current through it. Though all current-carrying, conductors produce magnetic fields, an electromagnet is usually constructed in such a way as to maximize the strength of the magnetic field it produces for a special purpose. Electromagnets find frequent application in research, industry, medical, and consumer products.

As an electrically controllable magnet, electromagnets find application in a wide variety of “electromechanical” devices: machines that effect mechanical force or motion through electrical power. Perhaps the most obvious example of such a machine is the electric motor.

Another example is the relay, an electrically controlled switch. If a switch contact mechanism is built so that it can be actuated (opened and closed) by the application of a magnetic field, and an electromagnet coil is placed in the near vicinity to produce that requisite field, it will be possible to open and close the switch by the application of a current through die coil. In effect, this gives us a device that enables electricity to control electricity.

Relays can be constructed to actuate multiple switch contacts, or operate them in “reverse” (energizing the coil will open the switch contact and unpowering the coil will allow it to spring closed again).

Задание 2. Ответьте на вопросы к тексту:

1. Was the discovery of the relationship between magnetism and electricity like many other scientific discoveries?

2. How did Oersted manage to produce a definite motion of the compass needle in response to the current?

3. What does the left-hand rule say?

4. What is the amount of magnetic field force generated by a coiled wire proportional to?

5. Where do electromagnets find frequent application?

Задание 3. Заполните пропуски предлогами:

1. Danish physicist Hans Christian Oersted was lecturing one day ... 1820 ... the possibility of electricity and magnetism being related ... one another, and demonstrated it... experiment... front ... his whole class!

2. ... order ... create a stronger magnetic field force ... with the same
amount... electric current, the wire can be wrapped ... a coil shape.

3. Magnetomotive force is very similar ... electromotive force ... an electric circuit.

4. A switch can be opened or closed ... the application ... the magnetic field, if an electromagnet coil is placed ... the near vicinity ... produce that requisite field.

5. An. electromagnet is usually constructed ... such a way......maximize the strength ... the magnetic field it produces ... specialpurpose.

Задание 4. Кратко изложите содержание текста, выскажите свое мнение.

 

[Литература: 1-4]

 

 




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