Tuesday, 3 February 2015

Study At Sweden


If you are going to study at a Swedish educational institution for more than 3 months, you must  have to apply for a residence permit for studies. During Rises studying for three months, you should apply for a visa.

You must show that you have money for your support throughout your scheduled study time, ie the corresponding 7 300 SEK / month for 10 months per year. For example, by submitting a certificate from the bank, you confirm that you have such financial means.
What is required for a residence permit application must be complete?

1. Completed application (a special form No. 104031 or 105031 in duplicate). The forms must be completed in English or Swedish.

2. Foreign Passport and copy of the ID page of passport (two copies).

3. Admission decision (+ copy).

4. Purchase fee (note that those who received a scholarship from the Swedish Institute or another
Swedish organization for studies in Sweden, is exempt from the fee).

5. Comprehensive sickness insurance cover in Sweden if you will be studying for less than one year at university / college.

Characteristics And Properties of Fluorine


Fluorine chemical element of atomic number 9, atomic weight 19.00 (he knows only one stable isotope, 199F). At room temperature is presented as a pale yellow gas, capable of liquefying only at very low temperature (-188 ° C at normal pressure). It is part of the group of the halogens, which constitutes the first member; is the most electronegative element, it shows a remarkable chemical reactivity and in fact is combined, directly or indirectly, with all elements (except with helium, argon and the neo) forming compounds, some of which are in turn equipped with easy to retain full activity, while others are exceptionally inert and stable. Many metals are attacked by the f., While some others form protective surface layers that prevent the progress of the attack to the underlying layers; so, as the lead reacts vigorously cold, aluminum, iron, chromium, nickel passivano for formation of stable protective veils cold; copper and gold are almost not at all attached.

The fluorination is the operation with which are introduced one or more atoms of f. in an organic compound. Several methods are: the most used consists in replacing the atoms of f. to atoms of other halogens already present in the molecule, and as agents for this operation using the tri- and antimony pentafluoride, hydrogen fluoride, fluoride, mercury or potassium. Other methods, of more limited application, are those of the electrolysis of a solution of hydrofluoric acid of the organic compound to be fluorinated and that of diazotization of an amine followed by decomposition of the diazonium salt to form the fluoride (method but of course only applies to aromatic compounds). Today the fluorination is widely used in the chemical industry, because the compounds that are obtained typically have exceptional properties of chemical and thermal stability.

The term fluorination is also used to indicate the coating of the outer surfaces of the lenses of optical instruments with an extremely thin layer of magnesium fluoride or cryolite, which allows to reduce 1-3% passive reflections, which amounted to about 4-7% of the transmitted light.

The Laws Of Electricity


We know that the potential difference ΔV from the generator starts moving electric charges in a circuit giving raise to an electric current. At constant applied potential difference, the current i that passes in a circuit depends on the characteristics of the conductive material that is used. Each conductor actually manifests a certain resistance to the passage of the current, due to collisions between the electrons in motion inside the conductor and the atoms of the impurities present in the circuit.

In mathematical terms, is defined as the resistance R of a conductor the ratio of the potential difference ΔV applied and the intensity of the current, ie R = ΔV / i. Since the current i appears in the denominator we have that in a conductor with high resistance R circulates a small current i, vice versa, a conductor with a small resistance R is characterized by the high currents. We can say that the resistance R measures the degree of opposition they meet the electrons to move up the potential difference ΔV. The unit of resistance is the ohm (Ω symbol, capital omega): 1 Ω = 1 V / 1 A.

In general, as the potential difference ΔV increases also the current i but there are various possible relationships between i and ΔV depending on the conductor that we take into consideration.
So if we measure with a voltmeter and the potential difference ΔV with an ammeter, the current i discover that in a metal the relationship R = ΔV / i is constant. In metallic conductors the resistance does not depend on the potential difference ΔV that we apply to the conductor. What determines then the resistance in a metallic conductor? The answer is given by the second law of Ohm. The resistance R in a conductor depends upon the material it is made of the wire, its length from its the section A. More precisely, we will have that R = ρ L / A, ie, the resistance is directly proportional to the length l of the wire and inversely proportional to the area of the section. The proportionality constant ρ (symbol that corresponds to the Greek letter ro) depends on the type of metal that we take into consideration and goes under the name of resistivity.
Resistivity small mean small resistance, ie good ability to conduct electricity. Since ρ = R • A / l, the unit of measurement of the resistivity in the International System is the ohm per meter (Ω • m).