The discovery of radioactivity

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Part I (4100)

Metamorphic Rocks

Heat and pressure deep beneath Earth’s surface can change any rock into metamorphic rock. The word metamorphic comes from the Greek words meta, meaning “change”, and morphosis, meaning “form”. When rock changes into metamorphic rock, its appearance, texture, crystal structure, and mineral content change. Metamorphic rock can form out of igneous, sedimentary, or other metamorphic rock. Collisions between Earth’s plates can push the rock down toward the heat of the mantle. Pockets of magma rising through the crust also provide heat that can produce metamorphic rocks. The deeper a rock is buried in the crust, the greater the pressure on that rock. Under high temperature and pressure many times greater than at Earth’s surface, the minerals in a rock can be changed into other minerals. The rock has become a metamorphic rock (830).

Transformers

One of the great advantages in the use of the alternating current is the ease with which the voltage may be changed by means of a relatively simple device known as a transformer. Although there are many different types of transformers and a great variety of applications, the principles of action are the same in each case.The transformer is a device for changing the electric current from one voltage to another. The key parts are: an iron core, two coils of insulated windings.It is used for increasing or decreasing voltage. So the function of a transformer is to change voltage and current of an alternating system to meet requirements of the equipment used. It is known to be simple in construction that it involves no moving parts. Transformers change voltage through electromagnetic induction(801).

Types of transformers

There are different types of transformers. By the purpose they are classified into step-up transformers and step-down transformers. In a step-up transformer the output voltage is larger than the input voltage, because the number of turns on the secondary winding is greater than that of the primary. In a step-down transformer the output voltage is less than input voltage as the number of turns on the secondary is fewer than that on the primary.By the construction transformers are classified into core-type and shelltype transformers. In the core-type transformers the primary and the secondary coils surround the core. Electrically they are equivalent, the difference is in the mechanical construction.By the methods of cooling transformers are classified into air-cooled, oil-cooled and water-cooled transformers (820).

Lubrication system

The service life of the automobile greatly depends on the maintenance of the lubrication system. The basic purpose of lubrication is to reduce the friction between moving surfaces.If parts rubbing on each other are not separated by a film or lubricant, the surface will rub and rapidly wear away. The frictional force depends upon the nature of the surface and also on the kind of material. The rougher the surface and the softer the material, the greater the friction. The more friction there is, the greater the loss of power, as it requires power to overcome friction. The principal parts of the engine needing lubrication are the main crankshaft bearings, connecting-rod bearings pins, camshaft bearings, piston and cylinder walls. For engine lubrication, mineral or petroleum oil is used almost exclusively(812).

Mechanical Engineering

Engineers in this field design, test, build, and operate machinery of all types; they also work on a variety of manufactured goods and certain kinds of structures. The field is divided into machinery, mechanisms, materials, hydraulics, and pneumatics; and heat as applied to engines, work and energy, heating, ventilating, and air conditioning. The mechanical engineer, therefore, must be trained in mechanics, hydraulics, and thermodynamics and must know such subjects as metallurgy and machine design. They specialise in particular types of machines such as pumps or steam turbines. A mechanical engineer designs not only the machines that make products but the products themselves, and must design for both economy and efficiency. A typical example of mechanical engineering is the design of a car or an agricultural machine(828).

Part II (4200)

Electronic engineering

Electronic engineering deals with the research, design, integration, and application of circuits and devices used in the transmission and processing of information. Information is now generated, transmitted, received, and stored electronically on a scale unprecedented in history, and there is every indication that the explosive rate of growth in this field will continue unabated. Engineers design circuits to perform specific tasks, such as amplifying electronic signals, adding binary numbers, and demodulating radio signals to recover the information they carry. Circuits are also used to generate waveforms useful for synchronization and timing, as in television, and for correcting errors in digital information.The electronics revolution set the trend towards integrating electronic devices on a tiny chip of silicon (826).

Friction

Friction occurs to some degree in almost all situations involving physical objects. In many cases, such as in a running automobile engine, it hinders a process. Friction between the moving parts of an engine resists the engine’s motion and turns energy into heat, reducing the engine’s efficiency. Friction also makes it difficult to slide a heavy object, such as a refrigerator, along the ground. In other cases, friction is helpful. Between people’s shoes and the ground it allows people to walk by pushing off the ground without slipping. On a slick surface, such as ice, shoes slip and slide instead of gripping because of the lack of friction, making walking difficult. It allows car tires to grip and roll along the road without skidding. Friction between nails and beams prevents the nails from sliding out and keeps buildings standing (843).

The reciprocating engine

The reciprocating engine consists of a series of pistons connected to a rotating crankshaft. As the pistons move up and down, the crankshaft rotates. The engine gets its name from the back-and-forth movement of its internal parts. The four-stroke engine is the most common type, and refers to the four different cycles the engine under goes to produce power. When the piston moves away from the cylinder head on the intake stroke, the intake valve opens and a mixture of fuel and air is drawn into the combustion chamber. As the cylinder moves back towards the cylinder head, the intake valve closes, and the fuel/air mixture is compressed. When compression is nearly complete, the spark plugs fire and the mixture is ignited to begin the power stroke. The expanding gases drive the piston away from the cylinder head, providing power to rotate the crankshaft (860).

The discovery of radioactivity

It was due more or less to an accident. Once in 1896, professor of physics Becquuerel obtained a preparation of Uranium bisulphate for the purpose of studying the phosphorescence of this substance. But his interests were drawn in some other direction;he put the material into his table.It happened that in his table there was a box containing some unexposed photographic plates, the ampoule of uranium bisulphate fell right on top of that box, remaining there for several weeks. Intending to take some photographs, Becquuerel opened the table, pushed aside the ampoule with the forgotten preparation; took out the box with the plates. But when he developed his photographs, he found that the plates were spoiled, as if they had been previously exposed to light. It was strange since the plates had been wrapped in thick black paper and never opened (852).