Text 3.1 Electromagnetic Induction. Electromagnetic Waves.
1. Magnetic Flux.
2. SI unit of magnetic flux.
3. Ostrogradsky-Gauss Theorem for Magnetic Field.
4. Inductance of Loop.
5. Work Done on Alteration of Magnetic Flux through Loop.
6. Electromagnetic Induction.
7. Eddy Electric Field.
8. Main Law of Electromagnetic Induction (Faraday’s Law).
9. Lenz’s Law.
10. Self-Induction.
11. Mutual Inductance. Transformers.
12. Magnetic Field Energy for Loop with Current.
13. Energy Density of Magnetic Field.
14. Displacement Current.
15. Electromagnetic Field.
16. Electromagnetic wave.
17. Maxwell’s Equations in Integral Form.
Home task
Task 1.
A charged particle moves in a magnetic field around a circular trajectory at a velocity of 106 m/s. The induction of the magnetic field is 0.3 T. The radius of the circle is 4 cm. Find the charge of the particle if its energy is 12 keV.
Task 2.
A frame rotates uniformly with an angular velocity of 15 rad/s in a homogeneous magnetic field having an induction of 0.8 T. The area of a frame is 150 cm2. The axis of rotation is in the plane of frame and forms an angle of 30o with the direction of the magnetic field force lines. Find the maximum value induction EMF in the rotating frame.
Task 3.
How many turns does a coil have if its inductance L=0.001 H and the magnetic flux through the coil Ф = 2×10-8 Wb at a current of 1 A?
Task 4.
A
core is inserted into a solenoid 50 cm long. The core is made of iron
for which the relation
is
unknown. The number of turns per unit length of the solenoid is 400
and its cross-sectional area is 10 cm2.
a) Find the permeability of the core when a current of 5 A flows
through the solenoid winding. Under these conditions, the magnetic
flux penetrating the cross-sectional area of the solenoid with thew
core is equal to 1.6×10-3
Wb. B) Find the inductance of the solenoid under these conditions.
HOME – READING
ELECTRICITY AND MAGNETISM
Electricity and magnetism are manifestations of the phenomenon of electromagnetism. Sometimes we can think of electricity and magnetism separately; at other times, we can understand them only as electromagnetic phenomenon, as with an electric motor. However, an electric current can produce magnetic forces, and magnets can produce electric currents. Electrical effects can be explained by the structure of the atom. Of the three basic building blocks of the atom — the proton, neutron, and electron — only two, the electron and proton, have electrical charges. Positively charged protons are in the nucleus of the atom, and the negatively charged electrons move around the nucleus. An atom has no charge because the number of electrons balances the number of protons. However, electrons have less mass than protons and move more readily. The outermost electrons of some atoms can be easily pulled away. When an atom loses electrons, it becomes a positively charged ion. If it gains electrons, it becomes a negatively charged ion. It is such charged particles that are the basis of electricity.
In static electricity, electric charges are transferred from one object to another. The change always involves the movement of electrons, never protons. If the charge is due to an excess of electrons, the object has a negative charge. If the charge is due to a shortage of electrons, the object has a positive charge.
Current electricity involves the movement of some of the electrons in a material. The movement of electrons through a circuit can be compared with the flow of water through pipes. A closed or complete circuit is one in which the free electrons leave the negative terminal of the battery, flow through the wires and bulbs, and return to the positive terminal of the battery.
Conductors consist of atoms whose outer electrons are loosely held and can move freely. The free electrons in a conductor move about in all directions when there is no current. However, when a potential difference is present, some of the electrons move in the same direction producing a current.
LESSON 4
TEXT 4.1.: FAMOUS PEOPLE OF SCIENCE AND ENGINEERING
Sikorsky Igor Ivanovich was a well-known aircraft engineer and manufacturer.
Sikorsky was born in 1889 in Kiev, in the Ukraine, and got his education at the naval college in St. Petersburg, and later in Kiev and Paris. He was the first to make experiments in helicopter design. In 1913 he designed, built, and flew the first successful aeroplane. Later he built military aircrafts for Russia and France.
In 1919 Sikorsky moved to the United States and later helped to organize an aircraft company that produced series of multiengine flying boats for commercial service. Sikorsky became an American citizen in 1928. In the late 1930s he returned to developing helicopters and produced the first successful helicopter in the west. Helicopters designed by Sikorsky were used mostly by the US Army Air Forces during World War II. He died in 1972 at the age of 83.
Tupolev Andrey Nikolayevich, famous aircraft was born in 1888. He graduated from the Moscow Higher Technical School, where he designed the first Russian wind tunnel. He helped to found the Central Aerohydrodynamics Institute in 1918 and later worked as the head of its design bureau. During his career directed the design of more than 100 military and commercial aircraft, including the TU-2 and TU-4 bombers used in the World War [I. In 1955 he designed
TU-104 the first passenger jet airliner. His TU-144 jet liner began its commercial passenger flights in 1977.
TEXT 4.2.: MECHANICAL PROPERTIES OF
MATERIALS
Materials Science and Technology is the study of materials and how they can be fabricated to meet the needs of modern technology. Using the laboratory techniques and knowledge of physics, chemistry, and metallurgy, scientists are finding new ways of using metals, plastics and other materials.
Engineers must know how materials respond to external forces, such as tension, compression, torsion, bending, and shear. All materials respond to these forces by elastic deformation. That is, the materials return their original size and form when the external force disappears. The materials may also have permanent deformation or they may fracture. The results of external forces are creep and fatigue.
Compression is a pressure causing a decrease in volume. When a material is subjected to a bending, shearing, or torsion (twisting) force, both tensile and compressive forces are simultaneously at work. When a metal bar is bent, one side of it is stretched and subjected to a tensional force, and the other side is compressed.
Tension is a pulling force; for example, the force in a cable holding a weight. Under tension, a material usually stretches, returning to its original length if the force does not exceed the material’s elastic limit. Under larger tensions, the material does riot return completely to its original condition, and under greater forces the material ruptures.
Fatigue is the growth of cracks under stress. It occurs when a mechanical part is subjected to a repeated or cyclic stress, such as vibration. Even when the maximum stress never exceeds the elastic limit, failure of the material can occur even after a short time. No deformation
seen during fatigue, but small localised cracks develop and propagate through the material until the remaining cross sectional area cannot support the maximum stress of the cyclic force. Knowledge of tensile stress, elastic limits, and the resistance of materials to creep and fatigue are of basic importance ii engineering.
Creep is a slow, permanent deformation that results from a steady force acting on a material. Materials at high temperatures usually suffer from this deformation. The gradual loosening of bolts and the deformation of components of machines and engines are all the examples of creep. In many cases the slow deformation stops because deformation eliminates the force causing the creep. Creep extended over a long time finally leads to the rupture of the material.
VOCABULARY
bar – брусок, засув
completely – повністю, досконалий
compression – стискання
creep – повзати
cross-sectional area-площа поперечного перерізу
cyclic stress – циклічна напруга
decrease – зменшення
elastic deformation – еластична деформація
elastic limit – межа еластичності
exceed – перевищувати
external forces – зовнішні сили
fatigue – втомлення металу
fracture – перелом, злам
loosen – послаблювати, слабнути
permanent deformation – постійна деформація
remaining – залишатися
shear – зріз
simultaneously – одночасно
to stretch – розтягувати
technique – методи
tension – напруженість
to propagate – розповсюджувати (ся)
to bend – гнути, згинати
to extend – простиратися, продовжуватися
to meet the needs – відповідати вимогам
to occur – походити
to respond – відповідати, реагувати
to suffer – страждати
torsion – кручення
twisting – скручування, згин
GENERAL UNDERSTANDING:
1.What are the external forces causing the elastic deformation of materials? Describe those forces that change the form and size of materials.
2.What are the results of external forces?
3.What kinds of deformation are the combinations of tension and compression?
4.What is the result of tension? What happens if the elastic limit of material is exceeded under tension?
5.What do we call fatigue? When does it occur? What are the results of fatigue?
6.What do we call creep? When does this type of permanent deformation take place? What are the results of creep?
HOME – READING
SCIENCE OF THE HEART
It is the most widely prescribed medical test in the United States. And no wonder. The electrocardiogram tells the inside story of how that most vital of organs, the heart, goes about its work of pumping the nourishing blood of life throughout the body.
Ninety-one years have passed since Willem Einthoven, a Dutch physician-physiologist invented the first practical way to measure what happens when the heart beats. By graphically tracing the electrical impulses that spark the heart's action, he opened the field of electrocardiography. In the decades since, many pioneers have improved on Einthoven's invention, and today an electrocardiogram offers detailed and precise information on the condition and performance of the heart.
This year, Wyeth-Ayerst pays special tribute to the medical heroes who made this possible. Twelve of them are pictured in a special 1992 calendar distributed to cardiologists. The calendar is part of the company's marketing program for a trio of drugs to treat the arrhythmias that electrocardiography detects. Arrhythmias are variations from the normal heart beat and are the principal reason a physician orders an electrocardiogram, or ECG.
"The ECG is a simple test for a patient" said Marc W. Deitch, M. D., Vice President of Medical Affairs and Medical Director of Wyeth-Ayerst Laboratories. "It's quick, painless, and there is little risk. Because it identifies otherwise invisible heart conditions, the ECG has become an irreplaceable part of medical diagnosis".
Sometimes variations in heart rhythm are normal, and may be caused by exercise, caffeine, alcohol, drugs, or congenital defects. Everyone experiences these to some degree. But when arrhythmias occur frequently, they put a strain on the heart by making it work harder to maintain normal blood flow.
Electrocardiograms help to detect these problems; antiarrhythmic drugs work to correct them. Wyeth-Ayerst offers three such medications. In fact, "Wyeth-Ayerst is the market leader in the antiarrhythmic arena", said Bob Czenszak, Group Product Director for the antiarrhythmic brands.
LESSON 5
TEXT 5.1.: MECHANICAL PROPERTIES OF MATERIALS
Density (specific weight) is the amount of mass in a unit volume. It is measured in kilograms per cubic metre. The density of water is 1000 kg/ m3 but most materials have a higher density and sink in water. Aluminium alloys, with typical densities around 2800 kg/ m3 are considerably less dense than steels, which have typical densities around 7800 kg/ in3. Density is important in any application where the material must not be heavy.
Stiffness (rigidity) is a measure of the resistance to deformation such as stretching or bending. The Young modulus is a measure of the resistance to simple stretching or compression. It is the ratio of the applied force unit area (stress) to the fractional elastic deformation (strain). Stiffness is important when a rigid structure is to be made.
Strength is the force per unit area (stress) that a material can support without failing. The units are the same as those of stiffness, MN/m2, but in this case the deformation is irreversible. The yield strength is the stress at which a material first deforms plastically. For a metal the yield strength may be less than the fracture strength, which is the stress at which it breaks. Many materials have a higher strength in compression than in tension.
Ductility is the ability of a material to deform with- out breaking. One of the great advantages of metals is their ability to be formed into the shape that is needed, such as car body parts. Materials that are not ductile are brittle. Ductile materials can absorb energy by deformation but brittle materials cannot.
Toughness is the resistance of a material to breaking when there is a crack in it. For a material of given toughness, the stress at which it will fail is inversely proportional to the square root of the size of the largest defect present. Toughness is different from strength: the toughest steels, for example, are different from the ones with highest tensile strength. Brittle materials have low toughness: glass can be broken along a chosen line by first scratching it with a diamond. Composites can be designed to have considerably greater toughness than their constituent materials. The example of a very tough composite is fiberglass that is very flexible and strong.
Creep resistance is the resistance to a gradual permanent change of shape, and it becomes especially important at higher temperatures. A successful research has been made in materials for machine parts that operate at high temperatures and under high tensile forces without gradually extending, for example the parts of plane engines.
VOCABULARY
ability – здатність
amount – кількість
absordb– поглинати
application – примінення
brittle – крихкий, ламкий
car body – капот автомобиля
constituent – компонент
crack – тріщина
creep resistance –стійкість до опору
definition – определение
dencity – щільність
ductility – ковкість, еластичність
failure – пошкодження
gradual – послідовний
permanent – постійний
rigid – жорсткий
to sink – тонути
square root – квадратний корінь
stiffness – жорсткий
strain – навантаження, напруга, деформація
strength – сила, міцність
stress – тиск, напруга
tensity strength – прочність на міцність
toughness – стійкість
yield strength – стійкість, текучість
Young modulus – модуль Юнга
General understanding:
What is the density of a material?
What are the units of density? Where low density is needed?
What are the densities of water, aluminum and steel?
A measure of what properties is stiffness? When stiffness is important?
What is Young modulus?
What is strength?
What is yield strength? Why fracture strength is always greater than yield strength?
What is ductility? Give the examples of ductile materials. Give the examples of brittle materials.
What is toughness?
What properties of steel are necessary for the manufacturing.
Text 5.2.