How magnetism makes current

I. Прочитайте и запомните следующие слова и словосочетания

circular field line	круговая силовая линия поля
to involve	1) вовлекать, затрагивать; 2) повлечь за собой ; 3) включать в себя, предполагать, подразумевать
clamp	зажим, тиски
to induce	1) индуктировать; 2) вызывать, стимулировать
flywheel	маховое колесо, маховик
axis	1) ось, осевая линия; 2) координата; 3) вал
application	1) применение, использование; 2) приложение; 3) наложение поля
mercury	ртуть
rim	1) обод, закраина; 2) зубчатый венец

II. Прочитайте и переведите текст How magnetism makes current

Electric current produces a magnetic field. The magnetic field can be visualized as a pattern of circular field lines surrounding the wire.

Electric current can be directly measured with a galvanometer, but this method involves breaking the circuit, which is sometimes inconvenient. Current can also be measured without breaking the circuit by detecting the magnetic field associated with the current. Devices used for this include Hall effect sensors, current clamps, current transformers, and Rogowski coils.

According to Ampère's law, an electric current produces a magnetic field.

Magnetism can make, or induce, electric current only when the conductor that carries the current and the lines of magnetic force move so that they cut across each other. The direction in which current flows in the moving conductor can be learned with Fleming's right hand rule for generators.

Basic Faraday disc generator

The device consists of a conducting flywheel rotating in a magnetic field with one electrical contact near the axis and the other near the periphery. It has been used for generating very high currents at low voltages in applications such as welding, electrolysis and railgun research. In pulsed energy applications, the angular momentum of the rotor is used to store energy over a long period and then release it in a short time.

In contrast to other types of generators, the output voltage never changes polarity. The charge separation results from the Lorentz force on the free charges in the disk. The motion is azimuthal and the field is axial, so the electromotive force is radial. The electrical contacts must be made through a "brush" or slip ring, which results in large losses at the low voltages generated. Some of these losses can be reduced by using mercury or other easily liquified metal (gallium) as the "brush", and a vertical-axis generator could allow the entire rim of a disk to be "brushed" by liquid metal. The table below shows the results of different relative motions of the parts of a circular homopolar generator.

magnet	disk	external indicating circuit	voltage indicated?
stationary	stationary	stationary	no
stationary	rotating	stationary	yes
stationary	stationary	rotating	yes
stationary	rotating	rotating	undetermined
rotating	stationary	stationary	no
rotating	rotating	stationary	yes
rotating	stationary	rotating	yes
rotating	rotating	rotating	undetermined

If the magnetic field is provided by a permanent magnet, the generator works regardless of whether the magnet is fixed to the stator or rotates with the disc. Before the discovery of the electron and the Lorentz force law, the phenomenon was inexplicable and was known as the Faraday paradox. The voltage is "undetermined" when both the indicator and the disk are rotated, regardless of whether the magnet is moving. There is an EMF and a nonuniform charge density, but no reaction of the indicator. An electric field is generated, but no voltage is brought out for display. This differs from the different relative motions of the parts of a rectilinear homopolar generator.

III. Ответьте на следующие вопросы, пользуясь информацией из текста

1. What produces a magnetic field?

2. How can electric current be measured?

3. In what case can magnetism induce electric current?

4. The output voltage often changes polarity, doesn’t it?

5. How can some losses be reduced?

IV. Дайте 3 формы следующих глаголов

To rise, to be, to take, to bring, to give, to win, to swim, to forget, to eat, to make

V. Заполните пропуски, используя глаголы в скобках

1. The method … breaking the circuit. (to involve)

2. The angular momentum … to store energy. ( to use)

3. The electrical contents must … through a slip ring. ( to make)

4. Before the discovery of the electron this phenomenon ... as Faraday paradox. ( to know)

5. The electromotive force … radial. ( to be)

VI. Дополните следующие предложения фактами из текста

1. The magnetic field can be visualized as…

2. The method of measuring electric current with a galvanometer involves…

3. Faraday disc generator consists of …

4. The charge separation results from …

5. The electrical contacts must be made through …

VII. Составьте все возможные виды вопросов на основе следующих предложений

1.These losses can be reduced by using mercury.

2. The molecules themselves are minute magnets.

3. The lines of magnetic force move so that they cut across each other.

4. On placing an unmagnetized iron bar near a strong magnet, we magnetize it.

5. At each point around the magnet, the magnetic field has both a strength and a direction.

VIII. Определите, какой частью речи являются неличные формы в следующих предложениях. Переведите предложения на русский язык

1. The device consists of a conducting flywheel rotating in a magnetic field.

2. The experiments having been made, we could discuss the results.

3. This method involves breaking the circuit.

4. Having experimented with electricity and magnetism, Gilbert wrote a book on magnetism.

5. It has been used for generating very high currents at low voltages.

IX. Расскажите , по-английски или по-русски , какая информация в тексте является для вас новой, а какая вам уже известна

Homereading

Прочитайте текст и определите, является ли утверждение истинным

The Sun and the Earth has similar magnetic fields.