Download Lesson 12. Topic “Magnetic effect of an electric current”. Grammar

Lesson 12.
Topic “Magnetic effect of an electric current”.
Grammar material: Prepositions.
Text: “Magnetic effect of an electric current”
The invention of the voltaic cell in 1800 gave electrical experiments a source of a
constant flow of current. Seven years later the Danish scientist and experimenter, Oersted,
decided to establish the relation between a flow of current and a magnetic needle. It took
him at least 13 years more to find out that a compass needle is deflected when brought
near a wire through which the electric current flows. At last, during a lecture he adjusted,
by chance, the wire parallel to the needle. Then, both he and his class saw that when the
current was turned on, the needle deflected almost at right angles towards the conductor.
As soon as the direction the needle was reserved, the direction the needle pointed in was
reserved too.
As seem in Fig. 5 the north end of the needle moves away from us when the current
flows from left to right. Oersted also pointed out that provided the wire were adjusted
below the needle, the deflection was reserved.
The above-mentioned phenomenon highly interested Ampere who repeated the
experiment and added a number of valuable observations and statements. He began his
research under the influence of Oersted’s discovery and carried through the rest of his life.
Everyone knows the rule thanks to which we can always find the direction of the
magnetic effect of the current. It is known as Ampere’s rule. Ampere established and
proved that magnetic effects could be produced without any magnets by means of
electricity alone. He turned his attention to the behaviour of the electric current in a single
straight conductor and in a conductor that is formed into a coil, i. e. a solenoid.
When a wire conducting a current is formed into a coil of several turns, the amount of
magnetism is greatly increased.
It is not difficult to understand that the greater the number of turns of wire, the greater
is the m.m.f. (that is the magnetomotive force) produced within the coil by any constant
amount of current flowing through it. In addition, when doubling the current, we double
the magnetism generated in the coil (see Fig. 6).
A solenoid has two poles which attract and repel the poles of other magnets. While
suspended, it takes up a north and a south direction exactly like the compass needle.
A core of iron becomes strongly magnetized if placed within the solenoid, while the
current is flowing.
When winding a coil of wire on an iron core we obtain an electromagnet. That the
electromagnet is a controllable and reliable magnet is perhaps known to everyone. It is, so
to say, a temporary magnet provided by electricity. Its behaviour is very simple. The
device is lifeless unless an electric current flows through the coil. However, the device
comes to life provided the current flows. The iron core will act as a magnet as long as the
current continues to pass along the winding.
TEST. Magnetic Effects of an Electric Current
I. Connect the word combinations:
static
effect
French
angles
iron
core
magnetic
cell
Ampere’s
charges
voltaic
physicist
right
rule
II. Choose the appropriate word from those in brackets:
1. Oersted decided (to establish, to make) the relation between a flow of current and a
magnetic needle.
2. Volta invented the first source of (constant, alternating) current in 1800.
3. When the current was (turned on, turned off) the needle deflected.
4. The current was reversed, the direction of the needle was (the same, reversed).
5. When the wire was adjusted below the needle the deflection was (reversed, the
same).
6. Ampere established that magnetic effects could be produced by means of (magnets,
electricity).
7. When a wire is formed into a coil the amount of magnetism is (decreased,
increased).
8. A core of iron is magnetized if placed (within, out of) the solenoid.
9. Electromagnet is a (permanent, temporary) magnet, provided by electricity.
III. Find the end of the sentences:
1. A current-carrying coil of wire
which is long in comparison with
its diameter…
2. When placing an iron core within
a solenoid…
3. Danish scientist and experimenter,
Oersted, decided to establish …
4. When a wire conducting a current
is formed into a coil of several turns…
5. The greater the number of turns
of wire…
6. A solenoid has 2 poles..
1.the greater is the m. m. f.
2. is a controllable and reliable magnet.
3. which attract and repel the poles of
other magnets.
4. the relation between a flow of current
and a magnetic needle.
5.is called a solenoid.
6.the amount of magnetism is greatly
increased.
7.we obtain an electromagnet.
8.the current continues to pass along
the winding.
7. The electromagnet …
8. The iron core will act as a magnet
as long as …
IV. Fill in the blanks with the words and phrases:
1. The temperature of boiling water does not change at … pressure.
2. The … of the electromagnet is usually made of iron.
3. The compass … always points to the North.
4. We must … the voltage before our experiment.
5. The magnetic and the electrical fields act … to each other.
6. If the resistance … the current in the circuit is reversed too.
7. Like poles of the magnet … each other.
8. The coil may contain several … of wire.18.Every evening I … TV … and watch the
news.
Grammar.
I. Choose the correct prepositions.
I'm Peter and I live … Germany. … summer I like to travel … Italy, because … the
weather and the people there. Last summer I took a plane … Munich to Rome. … the
airport we went to our hotel … bus. We stopped … a small restaurant for a quick meal.
The driver parked the bus … the restaurant. Nobody could find the bus and the driver, so
we waited … the restaurant … one hour. The driver was walking … the small park … the
restaurant which we did not know. So we were very angry … him. But my holidays were
great. We sat … campfires and went dancing … the early mornings.
II.Choose the correct preposition.
1) I'm tired … waiting for you.
2) He hasn't smoked … ages.
3) Nina is good … running.
4) I'm looking … my keys. Has anyone found them?
5) They dream … moving to South Africa.
6) This song was written … Madonna.
7) You can look the word … in a dictionary.
8) I can't come to the party. Don't wait … me.
9) She had problems … reading the instructions.
10) The police car chased the robbers … the streets.